From 6b1a18b2469ecc2f5252f7753ae54c39b6457a3c Mon Sep 17 00:00:00 2001
From: Stanislav Pankevich <s.pankevich@gmail.com>
Date: Wed, 20 Sep 2023 21:26:13 +0200
Subject: [PATCH] sdoc/grammar: introduce REFS/RELATIONS/ROLES

---
 docs/strictdoc_20_requirements.sdoc           |   66 +-
 docs/strictdoc_21_design.sdoc                 |    6 +-
 strictdoc/__init__.py                         |    2 +-
 .../excel/import_/excel_to_sdoc_converter.py  |   42 +-
 .../reqif/p01_sdoc/reqif_to_sdoc_converter.py |    4 +-
 .../p11_polarion/reqif_to_sdoc_converter.py   |    4 +-
 strictdoc/backend/reqif/sdoc_reqif_fields.py  |    2 +-
 strictdoc/backend/sdoc/grammar/grammar.py     |   22 +
 strictdoc/backend/sdoc/grammar/type_system.py |    2 +-
 strictdoc/backend/sdoc/models/constants.py    |    6 +
 .../backend/sdoc/models/document_grammar.py   |   53 +-
 strictdoc/backend/sdoc/models/reference.py    |   10 +-
 strictdoc/backend/sdoc/models/type_system.py  |   97 +-
 .../backend/sdoc/validations/requirement.py   |   54 +-
 strictdoc/backend/sdoc/writer.py              |  122 +-
 .../document_grammar_form_object.py           |    2 +-
 .../frame_document_grammar_edit.jinja.html    |    2 +
 strictdoc/server/routers/main_router.py       |    2 +-
 .../__init__.py                               |    0
 .../expected_output/Document_1.sdoc           |    0
 .../expected_output/dummy.txt                 |    0
 .../expected_output/strictdoc.toml            |    0
 .../input/dummy.txt                           |    0
 .../input/strictdoc.toml                      |    0
 .../sample.reqif                              |   10 +-
 .../test_case.py}                             |    0
 .../sample.reqif                              |   20 +-
 .../expected_output/document.sdoc             |    5 +-
 .../expected_output/document.sdoc             |    5 +-
 .../edit_grammar_add_new_field/__init__.py    |    0
 .../expected_output/document.sdoc             |    5 +-
 .../input/document.sdoc                       |    0
 .../test_case.py                              |    0
 .../expected_output/document.sdoc             |    5 +-
 .../expected_output/document.sdoc             |    5 +-
 .../expected_output/document.sdoc             |    5 +-
 .../expected_output/document.sdoc             |    5 +-
 .../expected_output/document.sdoc             |    2 +
 .../expected_output/document.sdoc             |    6 +-
 .../expected_output/document.sdoc             |    8 +-
 .../expected_output/document.sdoc             |    6 +-
 .../input/document.sdoc                       |    6 +-
 .../input/document2.sdoc                      |    6 +-
 .../input/document.sdoc                       |    6 +-
 .../expected_output/document.sdoc             |    6 +-
 .../input/document.sdoc                       |    6 +-
 .../expected/expected.sdoc                    |    7 +-
 .../p01_sdoc/end_to_end/13_refs/sample.sdoc   |    2 +-
 .../end_to_end/30_custom_grammar/sample.sdoc  |    2 +
 .../sample.sdoc                               |    2 +
 .../sample.sdoc                               |    2 +
 .../reqif/02_user_provided_example/script.py  |    2 +-
 tests/unit/helpers/test_document_builder.py   |    2 +-
 .../backend/sdoc/test_dsl_passthrough.py      | 1105 +++-------------
 .../sdoc/test_dsl_passthrough_grammar.py      | 1162 +++++++++++++++++
 .../backend/sdoc/test_dsl_passthrough_refs.py |  226 ++++
 56 files changed, 1984 insertions(+), 1143 deletions(-)
 rename tests/end2end/{screens/document/edit_document_grammar/edit_grammar_add_field => project_index/import_document_from_reqif/import_document_default_import}/__init__.py (100%)
 rename tests/end2end/project_index/import_document_from_reqif/{UC55_T01_default_import => import_document_default_import}/expected_output/Document_1.sdoc (100%)
 rename tests/end2end/project_index/import_document_from_reqif/{UC55_T01_default_import => import_document_default_import}/expected_output/dummy.txt (100%)
 rename tests/end2end/project_index/import_document_from_reqif/{UC55_T01_default_import => import_document_default_import}/expected_output/strictdoc.toml (100%)
 rename tests/end2end/project_index/import_document_from_reqif/{UC55_T01_default_import => import_document_default_import}/input/dummy.txt (100%)
 rename tests/end2end/project_index/import_document_from_reqif/{UC55_T01_default_import => import_document_default_import}/input/strictdoc.toml (100%)
 rename tests/end2end/project_index/import_document_from_reqif/{UC55_T01_default_import => import_document_default_import}/sample.reqif (100%)
 rename tests/end2end/project_index/import_document_from_reqif/{UC55_T01_default_import/test_UC55_T01_default_import.py => import_document_default_import/test_case.py} (100%)
 create mode 100644 tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_new_field/__init__.py
 rename tests/end2end/screens/document/edit_document_grammar/{edit_grammar_add_field => edit_grammar_add_new_field}/expected_output/document.sdoc (92%)
 rename tests/end2end/screens/document/edit_document_grammar/{edit_grammar_add_field => edit_grammar_add_new_field}/input/document.sdoc (100%)
 rename tests/end2end/screens/document/edit_document_grammar/{edit_grammar_add_field => edit_grammar_add_new_field}/test_case.py (100%)
 create mode 100644 tests/unit/strictdoc/backend/sdoc/test_dsl_passthrough_grammar.py
 create mode 100644 tests/unit/strictdoc/backend/sdoc/test_dsl_passthrough_refs.py

diff --git a/docs/strictdoc_20_requirements.sdoc b/docs/strictdoc_20_requirements.sdoc
index c8901651f..53eb90986 100644
--- a/docs/strictdoc_20_requirements.sdoc
+++ b/docs/strictdoc_20_requirements.sdoc
@@ -11,9 +11,6 @@ ELEMENTS:
   - TITLE: UID
     TYPE: String
     REQUIRED: False
-  - TITLE: REFS
-    TYPE: String
-    REQUIRED: False
   - TITLE: TITLE
     TYPE: String
     REQUIRED: True
@@ -26,6 +23,9 @@ ELEMENTS:
   - TITLE: COMMENT
     TYPE: String
     REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
+  - TYPE: File
 
 [FREETEXT]
 This document is a collection of high-level requirements for StrictDoc as well as some of its middle-level requirements. The existing requirements set is pending a proper functional decomposition/partitioning following the creation of bidirectional traces between the requirements and StrictDoc's source code.
@@ -36,13 +36,13 @@ TITLE: High-level requirements
 
 [REQUIREMENT]
 UID: SDOC-HIGH-REQS-MANAGEMENT
-REFS:
-- TYPE: Parent
-  VALUE: GOAL-1-TOOL-SUPPORT
 TITLE: Requirements management
 STATEMENT: >>>
 StrictDoc shall enable requirements management.
 <<<
+REFS:
+- TYPE: Parent
+  VALUE: GOAL-1-TOOL-SUPPORT
 
 [REQUIREMENT]
 UID: SDOC-HIGH-DATA-MODEL
@@ -127,11 +127,6 @@ TITLE: Data model
 
 [REQUIREMENT]
 UID: SDOC-DM-MODEL
-REFS:
-- TYPE: Parent
-  VALUE: SDOC-HIGH-REQS-MANAGEMENT
-- TYPE: Parent
-  VALUE: SDOC-HIGH-DATA-MODEL
 TITLE: Modeling capability
 STATEMENT: StrictDoc's Data Model shall accommodate for maximum possible standard requirement document formats.
 COMMENT: >>>
@@ -140,6 +135,11 @@ Examples of standard requirements documents include but are not limited to:
 - Non-nested requirement lists split by categories
   (e.g., Functional Requirements, Interface Requirements, Performance Requirements, etc.)
 <<<
+REFS:
+- TYPE: Parent
+  VALUE: SDOC-HIGH-REQS-MANAGEMENT
+- TYPE: Parent
+  VALUE: SDOC-HIGH-DATA-MODEL
 
 [SECTION]
 TITLE: Project
@@ -281,24 +281,24 @@ TITLE: SDoc file format
 
 [REQUIREMENT]
 UID: SDOC-FMT-PRIMARY
+TITLE: Primary text implementation
+STATEMENT: The SDoc format shall support encoding the Strict Doc Data Model in a plain-text human readable form.
 REFS:
 - TYPE: Parent
   VALUE: SDOC-DM-MODEL
-TITLE: Primary text implementation
-STATEMENT: The SDoc format shall support encoding the Strict Doc Data Model in a plain-text human readable form.
 
 [SECTION]
 TITLE: Grammar
 
 [REQUIREMENT]
 UID: SDOC-FMT-GRAMMAR
+TITLE: Grammar
+STATEMENT: The SDoc format shall be based on a fixed grammar.
 REFS:
 - TYPE: Parent
   VALUE: SDOC-HIGH-DATA-MODEL
 - TYPE: File
   VALUE: strictdoc/backend/sdoc/grammar/grammar.py
-TITLE: Grammar
-STATEMENT: The SDoc format shall be based on a fixed grammar.
 
 [REQUIREMENT]
 TITLE: No indentation
@@ -346,18 +346,18 @@ TITLE: Single document: Tabular form
 STATEMENT: StrictDoc shall export single document pages in a tabular form.
 
 [REQUIREMENT]
+TITLE: Single document: 1-level traceability
+STATEMENT: StrictDoc shall export 1-level traceability document.
 REFS:
 - TYPE: Parent
   VALUE: SDOC-HIGH-REQS-TRACEABILITY
-TITLE: Single document: 1-level traceability
-STATEMENT: StrictDoc shall export 1-level traceability document.
 
 [REQUIREMENT]
+TITLE: Single document: Deep traceability
+STATEMENT: StrictDoc shall export deep traceability document.
 REFS:
 - TYPE: Parent
   VALUE: SDOC-HIGH-REQS-TRACEABILITY
-TITLE: Single document: Deep traceability
-STATEMENT: StrictDoc shall export deep traceability document.
 
 [REQUIREMENT]
 TITLE: Left panel: Table of contents
@@ -376,11 +376,11 @@ STATEMENT: StrictDoc shall support exporting documents to Sphinx/RST format.
 
 [REQUIREMENT]
 UID: SDOC-GEN-EXCEL-EXPORT
+TITLE: Excel Export
+STATEMENT: StrictDoc shall support exporting documents to Excel format.
 REFS:
 - TYPE: File
   VALUE: strictdoc/backend/excel/export/excel_generator.py
-TITLE: Excel Export
-STATEMENT: StrictDoc shall support exporting documents to Excel format.
 
 [REQUIREMENT]
 TITLE: ReqIF import/export
@@ -393,15 +393,19 @@ TITLE: Validation
 
 [REQUIREMENT]
 UID: SDOC-VALIDATION-UNIQUE-UID
-REFS:
-- TYPE: Parent
-  VALUE: SDOC-HIGH-VALIDATION
 TITLE: Uniqueness of UID identifiers in a document tree
 STATEMENT: StrictDoc shall ensure that each UID used in a document tree is unique.
 COMMENT: This is implemented but the error message shall be made more readable.
+REFS:
+- TYPE: Parent
+  VALUE: SDOC-HIGH-VALIDATION
 
 [REQUIREMENT]
 UID: SDOC-VALIDATION-NO-CYCLES
+TITLE: No cycles in a document tree
+STATEMENT: >>>
+StrictDoc shall ensure that no requirements in document tree reference each other.
+<<<
 REFS:
 - TYPE: Parent
   VALUE: SDOC-HIGH-VALIDATION
@@ -409,19 +413,15 @@ REFS:
   VALUE: strictdoc/core/tree_cycle_detector.py
 - TYPE: File
   VALUE: strictdoc/core/traceability_index_builder.py
-TITLE: No cycles in a document tree
-STATEMENT: >>>
-StrictDoc shall ensure that no requirements in document tree reference each other.
-<<<
 
 [REQUIREMENT]
 UID: SDOC-VALIDATION-VALID-HTML
-REFS:
-- TYPE: Parent
-  VALUE: SDOC-HIGH-VALIDATION
 TITLE: Valid HTML markup
 STATEMENT: StrictDoc's HTML export tests shall validate the generated HTML markup.
 COMMENT: First candidate: Table of contents and its nested ``<ul>/<li>`` items.
+REFS:
+- TYPE: Parent
+  VALUE: SDOC-HIGH-VALIDATION
 
 [/SECTION]
 
@@ -476,11 +476,11 @@ TITLE: Implementation requirements
 
 [REQUIREMENT]
 UID: SDOC-IMPL-PARAL
+TITLE: Parallelization
+STATEMENT: StrictDoc shall enable parallelization of the time-consuming parts of the code.
 REFS:
 - TYPE: File
   VALUE: strictdoc/helpers/parallelizer.py
-TITLE: Parallelization
-STATEMENT: StrictDoc shall enable parallelization of the time-consuming parts of the code.
 
 [REQUIREMENT]
 UID: SDOC-IMPL-INCREMENTAL
diff --git a/docs/strictdoc_21_design.sdoc b/docs/strictdoc_21_design.sdoc
index 646e2e219..4cf7ae89e 100644
--- a/docs/strictdoc_21_design.sdoc
+++ b/docs/strictdoc_21_design.sdoc
@@ -140,9 +140,6 @@ ReqIF format does not seem to provide a dedicated convention for a text node to
 
 [REQUIREMENT]
 UID: SDOC_IMPL_2
-REFS:
-- TYPE: File
-  VALUE: strictdoc/helpers/parallelizer.py
 TITLE: SDOC_IMPL_2: Running out of semaphores on macOS
 STATEMENT: >>>
 This an edge case on macOS: Python crashes in the Parallelizer class when
@@ -159,5 +156,8 @@ The fragment of the crash:
     sl = self._semlock = _multiprocessing.SemLock(
     OSError: [Errno 28] No space left on device
 <<<
+REFS:
+- TYPE: File
+  VALUE: strictdoc/helpers/parallelizer.py
 
 [/SECTION]
diff --git a/strictdoc/__init__.py b/strictdoc/__init__.py
index 55a445cfe..3f63a442b 100644
--- a/strictdoc/__init__.py
+++ b/strictdoc/__init__.py
@@ -1,6 +1,6 @@
 from strictdoc.core.environment import SDocRuntimeEnvironment
 
-__version__ = "0.0.44a11"
+__version__ = "0.0.44a12"
 
 
 environment = SDocRuntimeEnvironment(__file__)
diff --git a/strictdoc/backend/excel/import_/excel_to_sdoc_converter.py b/strictdoc/backend/excel/import_/excel_to_sdoc_converter.py
index a83cc544e..531c09406 100644
--- a/strictdoc/backend/excel/import_/excel_to_sdoc_converter.py
+++ b/strictdoc/backend/excel/import_/excel_to_sdoc_converter.py
@@ -122,7 +122,11 @@ def create_document(title: Optional[str], extra_header_pairs) -> Document:
         document_title = title if title else "<No title>"
         document = Document(document_title, document_config, None, [], [])
 
-        fields = DocumentGrammar.create_default(document).elements[0].fields
+        fields = list(
+            DocumentGrammar.create_default(document).elements[0].fields
+        )
+        refs_index = len(fields) - 1
+
         for _, name in extra_header_pairs:
             fields.extend(
                 [
@@ -132,8 +136,14 @@ def create_document(title: Optional[str], extra_header_pairs) -> Document:
                 ]
             )
 
+        # Here, we want to make sure that the REFS grammar field still shows up
+        # in the grammar **after** all fields, including the custom fields.
+        # FIXME: The REFS field configuration will become a standalone entity
+        # in the grammar, it will not longer be kept inside the grammar fields.
+        fields.insert(len(fields) - 1, fields.pop(refs_index))
+
         requirements_element = GrammarElement(
-            parent=None, tag="REQUIREMENT", fields=fields
+            parent=None, tag="REQUIREMENT", fields=fields, relations=[]
         )
         elements = [requirements_element]
         grammar = DocumentGrammar(parent=document, elements=elements)
@@ -176,9 +186,21 @@ def create_requirement(
             tags=None,
             comments=comments,
         )
+        for i, name in columns.extra_header_pairs:
+            value = row_values[i].strip()
+            if value != "":
+                template_requirement.ordered_fields_lookup[name] = [
+                    RequirementField(
+                        parent=None,
+                        field_name=name,
+                        field_value=None,
+                        field_value_multiline=value,
+                        field_value_references=None,
+                    )
+                ]
         if parent_uid is not None:
             reference = ParentReqReference(
-                template_requirement, parent_uid, relation_uid=None
+                template_requirement, parent_uid, role_uid=None
             )
 
             requirement_field = RequirementField(
@@ -191,20 +213,6 @@ def create_requirement(
             template_requirement.ordered_fields_lookup["REFS"] = [
                 requirement_field
             ]
-
-        for i, name in columns.extra_header_pairs:
-            value = row_values[i].strip()
-            if value != "":
-                template_requirement.ordered_fields_lookup[name] = [
-                    RequirementField(
-                        parent=None,
-                        field_name=name,
-                        field_value=None,
-                        field_value_multiline=value,
-                        field_value_references=None,
-                    )
-                ]
-
         requirement = Requirement(
             parent=template_requirement.parent,
             requirement_type=template_requirement.requirement_type,
diff --git a/strictdoc/backend/reqif/p01_sdoc/reqif_to_sdoc_converter.py b/strictdoc/backend/reqif/p01_sdoc/reqif_to_sdoc_converter.py
index b92b769fa..2e5a64641 100644
--- a/strictdoc/backend/reqif/p01_sdoc/reqif_to_sdoc_converter.py
+++ b/strictdoc/backend/reqif/p01_sdoc/reqif_to_sdoc_converter.py
@@ -250,7 +250,7 @@ def create_grammar_element_from_spec_object_type(
             else:
                 raise NotImplementedError(attribute) from None
         requirement_element = GrammarElement(
-            parent=None, tag="REQUIREMENT", fields=fields
+            parent=None, tag="REQUIREMENT", fields=fields, relations=[]
         )
         return requirement_element
 
@@ -432,7 +432,7 @@ def create_requirement_from_spec_object(
                         parent_spec_object_parent.attribute_map[
                             foreign_key_id_or_none
                         ].value,
-                        relation_uid=None,
+                        role_uid=None,
                     )
                 )
             if len(parent_refs) > 0:
diff --git a/strictdoc/backend/reqif/p11_polarion/reqif_to_sdoc_converter.py b/strictdoc/backend/reqif/p11_polarion/reqif_to_sdoc_converter.py
index ed555767d..164a25766 100644
--- a/strictdoc/backend/reqif/p11_polarion/reqif_to_sdoc_converter.py
+++ b/strictdoc/backend/reqif/p11_polarion/reqif_to_sdoc_converter.py
@@ -279,7 +279,7 @@ def _p11_create_grammar_element_from_spec_object_type(
             else:
                 raise NotImplementedError(attribute) from None
         requirement_element = GrammarElement(
-            parent=None, tag="REQUIREMENT", fields=fields
+            parent=None, tag="REQUIREMENT", fields=fields, relations=[]
         )
         return requirement_element
 
@@ -442,7 +442,7 @@ def _p11_create_requirement_from_spec_object(
                         parent_spec_object_parent.attribute_map[
                             foreign_key_id_or_none
                         ].value,
-                        relation_uid=None,
+                        role_uid=None,
                     )
                 )
             if len(parent_refs) > 0:
diff --git a/strictdoc/backend/reqif/sdoc_reqif_fields.py b/strictdoc/backend/reqif/sdoc_reqif_fields.py
index 9d16a1ace..d6f3bdb2a 100644
--- a/strictdoc/backend/reqif/sdoc_reqif_fields.py
+++ b/strictdoc/backend/reqif/sdoc_reqif_fields.py
@@ -55,11 +55,11 @@ class ReqIFChapterField:
     "LEVEL",
     "STATUS",
     "TAGS",
-    "REFS",
     "ReqIF.Name",
     "ReqIF.Text",
     "RATIONALE",
     "NOTES",
+    "REFS",
     "ReqIF.ChapterName",
 ]
 
diff --git a/strictdoc/backend/sdoc/grammar/grammar.py b/strictdoc/backend/sdoc/grammar/grammar.py
index eb5f82f7d..fd11b5124 100644
--- a/strictdoc/backend/sdoc/grammar/grammar.py
+++ b/strictdoc/backend/sdoc/grammar/grammar.py
@@ -53,6 +53,28 @@
   '- TAG: ' tag = RequirementType '\n'
   '  FIELDS:' '\n'
   fields += GrammarElementField
+  (
+    '  RELATIONS:' '\n'
+    relations += GrammarElementRelation
+  )?
+;
+
+GrammarElementRelation[noskipws]:
+  (GrammarElementRelationParent | GrammarElementRelationChild | GrammarElementRelationFile)
+;
+
+GrammarElementRelationParent[noskipws]:
+  '  - TYPE: ' relation_type='Parent' '\n'
+  ('    ROLE: ' relation_role=/.+/ '\n')?
+;
+
+GrammarElementRelationChild[noskipws]:
+  '  - TYPE: ' relation_type='Child' '\n'
+  ('    ROLE: ' relation_role=/.+/ '\n')?
+;
+
+GrammarElementRelationFile[noskipws]:
+  '  - TYPE: ' relation_type='File' '\n'
 ;
 
 GrammarElementField[noskipws]:
diff --git a/strictdoc/backend/sdoc/grammar/type_system.py b/strictdoc/backend/sdoc/grammar/type_system.py
index 2f3ac60ea..dbf99799b 100644
--- a/strictdoc/backend/sdoc/grammar/type_system.py
+++ b/strictdoc/backend/sdoc/grammar/type_system.py
@@ -28,7 +28,7 @@
 ParentReqReference[noskipws]:
   '- TYPE: Parent' '\n'
   '  VALUE: ' ref_uid = /.*$/ '\n'
-  ('  RELATION: ' relation_uid = /.+$/ '\n')?
+  ('  ROLE: ' role_uid = /.+$/ '\n')?
 ;
 
 ChildReqReference[noskipws]:
diff --git a/strictdoc/backend/sdoc/models/constants.py b/strictdoc/backend/sdoc/models/constants.py
index 458752236..9c526402d 100644
--- a/strictdoc/backend/sdoc/models/constants.py
+++ b/strictdoc/backend/sdoc/models/constants.py
@@ -29,6 +29,9 @@
     GrammarElementFieldSingleChoice,
     GrammarElementFieldString,
     GrammarElementFieldTag,
+    GrammarElementRelationChild,
+    GrammarElementRelationFile,
+    GrammarElementRelationParent,
 )
 
 SECTION_MODELS = [
@@ -59,6 +62,9 @@
     GrammarElementFieldMultipleChoice,
     GrammarElementFieldTag,
     GrammarElementFieldReference,
+    GrammarElementRelationParent,
+    GrammarElementRelationChild,
+    GrammarElementRelationFile,
 ]
 DOCUMENT_MODELS.extend(SECTION_MODELS)
 
diff --git a/strictdoc/backend/sdoc/models/document_grammar.py b/strictdoc/backend/sdoc/models/document_grammar.py
index 114604824..bcdef3bd7 100644
--- a/strictdoc/backend/sdoc/models/document_grammar.py
+++ b/strictdoc/backend/sdoc/models/document_grammar.py
@@ -1,21 +1,43 @@
 from collections import OrderedDict, defaultdict
-from typing import Dict, List, Set
+from typing import Dict, List, Set, Union
 
 from strictdoc.backend.sdoc.models.type_system import (
     RESERVED_NON_META_FIELDS,
     GrammarElementField,
     GrammarElementFieldReference,
     GrammarElementFieldString,
+    GrammarElementRelationParent,
     GrammarReferenceType,
     RequirementFieldName,
 )
 
 
+def create_default_relations(parent) -> List[GrammarElementRelationParent]:
+    return [
+        GrammarElementRelationParent(
+            parent=parent,
+            relation_type="Parent",
+            relation_role=None,
+        )
+    ]
+
+
 class GrammarElement:
-    def __init__(self, parent, tag: str, fields: List[GrammarElementField]):
+    def __init__(
+        self,
+        parent,
+        tag: str,
+        fields: List[GrammarElementField],
+        relations: List,
+    ):
         self.parent = parent
         self.tag: str = tag
         self.fields: List[GrammarElementField] = fields
+        self.relations: List[Union[GrammarElementRelationParent]] = (
+            relations
+            if relations is not None and len(relations) > 0
+            else create_default_relations(self)
+        )
         fields_map: OrderedDict = OrderedDict()
         for field in fields:
             fields_map[field.title] = field
@@ -87,17 +109,6 @@ def create_default(parent):
             GrammarElementFieldString(
                 parent=None, title=RequirementFieldName.TAGS, required="False"
             ),
-            GrammarElementFieldReference(
-                parent=None,
-                title=RequirementFieldName.REFS,
-                types=[
-                    GrammarReferenceType.PARENT_REQ_REFERENCE,
-                    GrammarReferenceType.CHILD_REQ_REFERENCE,
-                    GrammarReferenceType.FILE_REFERENCE,
-                    GrammarReferenceType.BIB_REFERENCE,
-                ],
-                required="False",
-            ),
             GrammarElementFieldString(
                 parent=None,
                 title=RequirementFieldName.TITLE,
@@ -118,10 +129,24 @@ def create_default(parent):
                 title=RequirementFieldName.COMMENT,
                 required="False",
             ),
+            GrammarElementFieldReference(
+                parent=None,
+                title=RequirementFieldName.REFS,
+                types=[
+                    GrammarReferenceType.PARENT_REQ_REFERENCE,
+                    GrammarReferenceType.CHILD_REQ_REFERENCE,
+                    GrammarReferenceType.FILE_REFERENCE,
+                ],
+                required="False",
+            ),
         ]
         requirement_element = GrammarElement(
-            parent=None, tag="REQUIREMENT", fields=fields
+            parent=None, tag="REQUIREMENT", fields=fields, relations=[]
+        )
+        requirement_element.relations = create_default_relations(
+            requirement_element
         )
+
         elements: List[GrammarElement] = [requirement_element]
         grammar = DocumentGrammar(parent=parent, elements=elements)
         grammar.is_default = True
diff --git a/strictdoc/backend/sdoc/models/reference.py b/strictdoc/backend/sdoc/models/reference.py
index 81f0dc241..f8b1995c5 100644
--- a/strictdoc/backend/sdoc/models/reference.py
+++ b/strictdoc/backend/sdoc/models/reference.py
@@ -30,16 +30,14 @@ def get_file_format(self) -> Optional[str]:
 
 @auto_described
 class ParentReqReference(Reference):
-    def __init__(self, parent, ref_uid: str, relation_uid: Optional[str]):
+    def __init__(self, parent, ref_uid: str, role_uid: Optional[str]):
         super().__init__(ReferenceType.PARENT, parent)
         self.ref_uid: str = ref_uid
-        # When RELATION: field is not provided for a parent reference, the
+        # When ROLE: field is not provided for a parent reference, the
         # textX still passes relation_uid as an empty string (instead of None
         # as one could expect).
-        self.relation_uid: Optional[str] = (
-            relation_uid
-            if relation_uid is not None and len(relation_uid) > 0
-            else None
+        self.role_uid: Optional[str] = (
+            role_uid if role_uid is not None and len(role_uid) > 0 else None
         )
 
 
diff --git a/strictdoc/backend/sdoc/models/type_system.py b/strictdoc/backend/sdoc/models/type_system.py
index 471a73a6b..9585eb116 100644
--- a/strictdoc/backend/sdoc/models/type_system.py
+++ b/strictdoc/backend/sdoc/models/type_system.py
@@ -1,4 +1,4 @@
-from typing import List, Optional
+from typing import List, Optional, Union
 
 from pybtex.database import Entry
 
@@ -184,6 +184,54 @@ def __init__(self, parent, title: str, required: str):
         self.required: bool = required == "True"
 
 
+@auto_described
+class GrammarElementRelationParent:
+    def __init__(
+        self, parent, relation_type: str, relation_role: Optional[str]
+    ):
+        assert relation_type == "Parent"
+        self.parent = parent
+        self.relation_type = relation_type
+        self.relation_role: Optional[str] = (
+            relation_role
+            if relation_role is not None and len(relation_role) > 0
+            else None
+        )
+
+
+@auto_described
+class GrammarElementRelationChild:
+    def __init__(
+        self, parent, relation_type: str, relation_role: Optional[str]
+    ):
+        assert relation_type == "Child"
+        self.parent = parent
+        self.relation_type = relation_type
+        self.relation_role: Optional[str] = (
+            relation_role
+            if relation_role is not None and len(relation_role) > 0
+            else None
+        )
+
+
+@auto_described
+class GrammarElementRelationFile:
+    def __init__(self, parent, relation_type: str):
+        assert relation_type == "File"
+        self.parent = parent
+        self.relation_type = relation_type
+        self.relation_role: Optional[str] = None
+
+
+@auto_described
+class GrammarElementRelationBibtex:
+    def __init__(self, parent, relation_type: str):
+        assert relation_type == "Bibtex"
+        self.parent = parent
+        self.relation_type = relation_type
+        self.relation_role: Optional[str] = None
+
+
 @auto_described
 class GrammarElementFieldReference(GrammarElementField):
     def __init__(self, parent, title: str, types: List[str], required: str):
@@ -193,3 +241,50 @@ def __init__(self, parent, title: str, types: List[str], required: str):
         self.title: str = title
         self.types: List[str] = types
         self.required: bool = required == "True"
+
+    def convert_to_relations(
+        self,
+    ) -> List[
+        Union[
+            GrammarElementRelationParent,
+            GrammarElementRelationChild,
+            GrammarElementRelationFile,
+            GrammarElementRelationBibtex,
+        ]
+    ]:
+        relation_types: List[
+            Union[
+                GrammarElementRelationParent,
+                GrammarElementRelationChild,
+                GrammarElementRelationFile,
+                GrammarElementRelationBibtex,
+            ]
+        ] = []
+
+        for ref_type in self.types:
+            if ref_type == "ParentReqReference":
+                relation_types.append(
+                    GrammarElementRelationParent(
+                        self.parent, "Parent", relation_role=None
+                    )
+                )
+                continue
+            if ref_type == "ChildReqReference":
+                relation_types.append(
+                    GrammarElementRelationChild(
+                        self.parent, "Child", relation_role=None
+                    )
+                )
+                continue
+            if ref_type == "FileReference":
+                relation_types.append(
+                    GrammarElementRelationFile(self.parent, "File")
+                )
+                continue
+            if ref_type == "BibReference":
+                relation_types.append(
+                    GrammarElementRelationBibtex(self.parent, "Bibtex")
+                )
+                continue
+            raise NotImplementedError(ref_type)
+        return relation_types
diff --git a/strictdoc/backend/sdoc/validations/requirement.py b/strictdoc/backend/sdoc/validations/requirement.py
index e92532de3..6b669b03a 100644
--- a/strictdoc/backend/sdoc/validations/requirement.py
+++ b/strictdoc/backend/sdoc/validations/requirement.py
@@ -15,7 +15,6 @@
 )
 from strictdoc.backend.sdoc.models.type_system import (
     GrammarElementFieldMultipleChoice,
-    GrammarElementFieldReference,
     GrammarElementFieldSingleChoice,
     GrammarElementFieldTag,
     ReferenceType,
@@ -37,7 +36,7 @@ def validate_requirement(
         document_grammar.fields_order_by_type[requirement.requirement_type]
     )
     for field_name in requirement.ordered_fields_lookup:
-        if field_name not in registered_fields:
+        if field_name not in registered_fields and field_name != "REFS":
             raise StrictDocSemanticError.unregistered_field(
                 field_name=field_name,
                 requirement=requirement,
@@ -62,7 +61,18 @@ def validate_requirement(
         grammar_fields_iterator, None
     )
 
+    refs_requirement_field = None
+    refs_grammar_field = None
     while True:
+        if (
+            requirement_field is not None
+            and requirement_field.field_name == "REFS"
+        ):
+            refs_requirement_field = requirement_field
+            requirement_field = next(requirement_field_iterator, None)
+        if grammar_field is not None and grammar_field.title == "REFS":
+            refs_grammar_field = grammar_field
+            grammar_field = next(grammar_fields_iterator, None)
         try:
             valid_or_not_required_field = validate_requirement_field(
                 requirement,
@@ -83,6 +93,27 @@ def validate_requirement(
             assert not grammar_field.required
             grammar_field = next(grammar_fields_iterator, None)
 
+    # REFS validation.
+
+    if refs_requirement_field is not None and refs_grammar_field is not None:
+        requirement_field_value_references = (
+            refs_requirement_field.field_value_references
+        )
+        for reference in requirement_field_value_references:
+            if (
+                reference.ref_type in ReferenceType.GRAMMAR_REFERENCE_TYPE_MAP
+                and ReferenceType.GRAMMAR_REFERENCE_TYPE_MAP[reference.ref_type]
+                in refs_grammar_field.types
+            ):
+                continue
+            raise StrictDocSemanticError.invalid_reference_type_item(
+                requirement=requirement,
+                document_grammar=document_grammar,
+                requirement_field=refs_requirement_field,
+                reference_item=reference,
+                **get_location(requirement),
+            )
+
 
 def validate_requirement_field(
     requirement: Requirement,
@@ -162,23 +193,4 @@ def validate_requirement_field(
                 **get_location(requirement),
             )
 
-    elif isinstance(grammar_field, GrammarElementFieldReference):
-        requirement_field_value_references = (
-            requirement_field.field_value_references
-        )
-        for reference in requirement_field_value_references:
-            if (
-                reference.ref_type in ReferenceType.GRAMMAR_REFERENCE_TYPE_MAP
-                and ReferenceType.GRAMMAR_REFERENCE_TYPE_MAP[reference.ref_type]
-                in grammar_field.types
-            ):
-                continue
-            raise StrictDocSemanticError.invalid_reference_type_item(
-                requirement=requirement,
-                document_grammar=document_grammar,
-                requirement_field=requirement_field,
-                reference_item=reference,
-                **get_location(requirement),
-            )
-
     return True
diff --git a/strictdoc/backend/sdoc/writer.py b/strictdoc/backend/sdoc/writer.py
index 9b8512237..8e4495280 100644
--- a/strictdoc/backend/sdoc/writer.py
+++ b/strictdoc/backend/sdoc/writer.py
@@ -1,8 +1,10 @@
 from enum import Enum
+from typing import List, Optional
 
 from strictdoc.backend.sdoc.models.anchor import Anchor
 from strictdoc.backend.sdoc.models.document import Document
 from strictdoc.backend.sdoc.models.document_config import DocumentConfig
+from strictdoc.backend.sdoc.models.document_grammar import DocumentGrammar
 from strictdoc.backend.sdoc.models.inline_link import InlineLink
 from strictdoc.backend.sdoc.models.reference import (
     BibReference,
@@ -24,6 +26,7 @@
     RequirementFieldType,
 )
 from strictdoc.core.document_iterator import DocumentCachingIterator
+from strictdoc.helpers.cast import assert_cast
 
 
 class TAG(Enum):
@@ -103,7 +106,7 @@ def write(self, document):
                     output += requirement_in_toc
                     output += "\n"
 
-        document_grammar = document.grammar
+        document_grammar: DocumentGrammar = document.grammar
         if not document_grammar.is_default:
             output += "\n[GRAMMAR]\n"
             output += "ELEMENTS:\n"
@@ -111,8 +114,32 @@ def write(self, document):
                 output += "- TAG: "
                 output += element.tag
                 output += "\n  FIELDS:\n"
+                refs_field: Optional[GrammarElementFieldReference] = None
                 for grammar_field in element.fields:
+                    if grammar_field.title == "REFS":
+                        refs_field = assert_cast(
+                            grammar_field, GrammarElementFieldReference
+                        )
+                        continue
                     output += SDWriter._print_grammar_field_type(grammar_field)
+
+                relations: List = element.relations
+                assert len(relations) > 0, relations
+
+                # For backward compatibility, we print RELATIONS from REFS
+                # grammar field if it exists.
+                if not document_grammar.is_default and refs_field is not None:
+                    relations = refs_field.convert_to_relations()
+                output += "  RELATIONS:\n"
+
+                assert len(relations) > 0, relations
+                for element_relation in relations:
+                    output += f"  - TYPE: {element_relation.relation_type}\n"
+                    if element_relation.relation_role is not None:
+                        output += (
+                            f"    ROLE: {element_relation.relation_role}\n"
+                        )
+
         for free_text in document.free_texts:
             output += "\n"
             output += self._print_free_text(free_text)
@@ -190,6 +217,8 @@ def _print_requirement_fields(
         element = document.grammar.elements_by_type[
             section_content.requirement_type
         ]
+
+        refs_already_printed = False
         for element_field in element.fields:
             field_name = element_field.title
             if field_name not in section_content.ordered_fields_lookup:
@@ -206,43 +235,8 @@ def _print_requirement_fields(
                     output += "<<<"
                     output += "\n"
                 elif field.field_value_references:
-                    output += "REFS:"
-                    output += "\n"
-
-                    reference: Reference
-                    for reference in field.field_value_references:
-                        output += "- TYPE: "
-                        output += reference.ref_type
-                        output += "\n"
-
-                        if isinstance(reference, BibReference):
-                            ref: BibReference = reference
-                            output += "  FORMAT: "
-                            output += ref.bib_entry.bib_format
-                            output += "\n"
-                            output += "  VALUE: "
-                            output += ref.bib_entry.bib_value
-                            output += "\n"
-                        elif isinstance(reference, FileReference):
-                            ref: FileReference = reference
-                            file_format = ref.get_file_format()
-                            if file_format:
-                                output += "  FORMAT: "
-                                output += file_format
-                                output += "\n"
-                            output += "  VALUE: "
-                            output += ref.get_posix_path()
-                            output += "\n"
-                        elif isinstance(reference, ParentReqReference):
-                            ref: ParentReqReference = reference
-                            output += "  VALUE: "
-                            output += ref.ref_uid
-                            output += "\n"
-                            if reference.relation_uid is not None:
-                                output += "  RELATION: "
-                                output += ref.relation_uid
-                                output += "\n"
-
+                    output += SDWriter._print_requirement_refs(field)
+                    refs_already_printed = True
                 elif field.field_value is not None:
                     if len(field.field_value) > 0:
                         output += f"{field_name}: "
@@ -254,6 +248,17 @@ def _print_requirement_fields(
                     output += f"{field_name}: "
                     output += "\n"
 
+        if (
+            not refs_already_printed
+            and "REFS" in section_content.ordered_fields_lookup
+        ):
+            requirement_refs_fields = section_content.ordered_fields_lookup[
+                "REFS"
+            ]
+            output += SDWriter._print_requirement_refs(
+                requirement_refs_fields[0]
+            )
+
         return output
 
     @staticmethod
@@ -341,3 +346,44 @@ def print_free_text_content(free_text):
             else:
                 raise NotImplementedError(part)
         return output
+
+    @classmethod
+    def _print_requirement_refs(cls, field):
+        output = ""
+        output += "REFS:"
+        output += "\n"
+
+        reference: Reference
+        for reference in field.field_value_references:
+            output += "- TYPE: "
+            output += reference.ref_type
+            output += "\n"
+
+            if isinstance(reference, BibReference):
+                ref: BibReference = reference
+                output += "  FORMAT: "
+                output += ref.bib_entry.bib_format
+                output += "\n"
+                output += "  VALUE: "
+                output += ref.bib_entry.bib_value
+                output += "\n"
+            elif isinstance(reference, FileReference):
+                ref: FileReference = reference
+                file_format = ref.get_file_format()
+                if file_format:
+                    output += "  FORMAT: "
+                    output += file_format
+                    output += "\n"
+                output += "  VALUE: "
+                output += ref.get_posix_path()
+                output += "\n"
+            elif isinstance(reference, ParentReqReference):
+                parent_reference: ParentReqReference = reference
+                output += "  VALUE: "
+                output += parent_reference.ref_uid
+                output += "\n"
+                if parent_reference.role_uid is not None:
+                    output += "  ROLE: "
+                    output += parent_reference.role_uid
+                    output += "\n"
+        return output
diff --git a/strictdoc/export/html/form_objects/document_grammar_form_object.py b/strictdoc/export/html/form_objects/document_grammar_form_object.py
index 793fc4275..337da3a40 100644
--- a/strictdoc/export/html/form_objects/document_grammar_form_object.py
+++ b/strictdoc/export/html/form_objects/document_grammar_form_object.py
@@ -152,7 +152,7 @@ def convert_to_document_grammar(self) -> DocumentGrammar:
             )
             grammar_fields.append(grammar_field)
         requirement_element = GrammarElement(
-            parent=None, tag="REQUIREMENT", fields=grammar_fields
+            parent=None, tag="REQUIREMENT", fields=grammar_fields, relations=[]
         )
         elements: List[GrammarElement] = [requirement_element]
         grammar = DocumentGrammar(parent=None, elements=elements)
diff --git a/strictdoc/export/html/templates/screens/document/document/frame_document_grammar_edit.jinja.html b/strictdoc/export/html/templates/screens/document/document/frame_document_grammar_edit.jinja.html
index 5f49f6ee6..05340a553 100644
--- a/strictdoc/export/html/templates/screens/document/document/frame_document_grammar_edit.jinja.html
+++ b/strictdoc/export/html/templates/screens/document/document/frame_document_grammar_edit.jinja.html
@@ -19,7 +19,9 @@
 
     <sdoc-form-grid id="document__editable_grammar_fields">
       {%- for field in form_object.fields -%}
+        {%- if field.field_name != "REFS" -%}
         {%- include "screens/document/document/frame_document_grammar_edit_custom_field.jinja.html" -%}
+        {%- endif -%}
       {%- endfor -%}
     </sdoc-form-grid>
 
diff --git a/strictdoc/server/routers/main_router.py b/strictdoc/server/routers/main_router.py
index 19ac81c70..0c5bdf302 100644
--- a/strictdoc/server/routers/main_router.py
+++ b/strictdoc/server/routers/main_router.py
@@ -1036,7 +1036,7 @@ def __init__(self):
             ref_uid = reference_field.field_value
             references.append(
                 ParentReqReference(
-                    parent=requirement, ref_uid=ref_uid, relation_uid=None
+                    parent=requirement, ref_uid=ref_uid, role_uid=None
                 )
             )
         if len(references) > 0:
diff --git a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_field/__init__.py b/tests/end2end/project_index/import_document_from_reqif/import_document_default_import/__init__.py
similarity index 100%
rename from tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_field/__init__.py
rename to tests/end2end/project_index/import_document_from_reqif/import_document_default_import/__init__.py
diff --git a/tests/end2end/project_index/import_document_from_reqif/UC55_T01_default_import/expected_output/Document_1.sdoc b/tests/end2end/project_index/import_document_from_reqif/import_document_default_import/expected_output/Document_1.sdoc
similarity index 100%
rename from tests/end2end/project_index/import_document_from_reqif/UC55_T01_default_import/expected_output/Document_1.sdoc
rename to tests/end2end/project_index/import_document_from_reqif/import_document_default_import/expected_output/Document_1.sdoc
diff --git a/tests/end2end/project_index/import_document_from_reqif/UC55_T01_default_import/expected_output/dummy.txt b/tests/end2end/project_index/import_document_from_reqif/import_document_default_import/expected_output/dummy.txt
similarity index 100%
rename from tests/end2end/project_index/import_document_from_reqif/UC55_T01_default_import/expected_output/dummy.txt
rename to tests/end2end/project_index/import_document_from_reqif/import_document_default_import/expected_output/dummy.txt
diff --git a/tests/end2end/project_index/import_document_from_reqif/UC55_T01_default_import/expected_output/strictdoc.toml b/tests/end2end/project_index/import_document_from_reqif/import_document_default_import/expected_output/strictdoc.toml
similarity index 100%
rename from tests/end2end/project_index/import_document_from_reqif/UC55_T01_default_import/expected_output/strictdoc.toml
rename to tests/end2end/project_index/import_document_from_reqif/import_document_default_import/expected_output/strictdoc.toml
diff --git a/tests/end2end/project_index/import_document_from_reqif/UC55_T01_default_import/input/dummy.txt b/tests/end2end/project_index/import_document_from_reqif/import_document_default_import/input/dummy.txt
similarity index 100%
rename from tests/end2end/project_index/import_document_from_reqif/UC55_T01_default_import/input/dummy.txt
rename to tests/end2end/project_index/import_document_from_reqif/import_document_default_import/input/dummy.txt
diff --git a/tests/end2end/project_index/import_document_from_reqif/UC55_T01_default_import/input/strictdoc.toml b/tests/end2end/project_index/import_document_from_reqif/import_document_default_import/input/strictdoc.toml
similarity index 100%
rename from tests/end2end/project_index/import_document_from_reqif/UC55_T01_default_import/input/strictdoc.toml
rename to tests/end2end/project_index/import_document_from_reqif/import_document_default_import/input/strictdoc.toml
diff --git a/tests/end2end/project_index/import_document_from_reqif/UC55_T01_default_import/sample.reqif b/tests/end2end/project_index/import_document_from_reqif/import_document_default_import/sample.reqif
similarity index 100%
rename from tests/end2end/project_index/import_document_from_reqif/UC55_T01_default_import/sample.reqif
rename to tests/end2end/project_index/import_document_from_reqif/import_document_default_import/sample.reqif
index beb5bbc38..ce0e5570f 100644
--- a/tests/end2end/project_index/import_document_from_reqif/UC55_T01_default_import/sample.reqif
+++ b/tests/end2end/project_index/import_document_from_reqif/import_document_default_import/sample.reqif
@@ -37,11 +37,6 @@
                 <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
               </TYPE>
             </ATTRIBUTE-DEFINITION-STRING>
-            <ATTRIBUTE-DEFINITION-STRING IDENTIFIER="REFS" LONG-NAME="REFS">
-              <TYPE>
-                <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
-              </TYPE>
-            </ATTRIBUTE-DEFINITION-STRING>
             <ATTRIBUTE-DEFINITION-STRING IDENTIFIER="ReqIF.Name" LONG-NAME="ReqIF.Name">
               <TYPE>
                 <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
@@ -62,6 +57,11 @@
                 <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
               </TYPE>
             </ATTRIBUTE-DEFINITION-STRING>
+            <ATTRIBUTE-DEFINITION-STRING IDENTIFIER="REFS" LONG-NAME="REFS">
+              <TYPE>
+                <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
+              </TYPE>
+            </ATTRIBUTE-DEFINITION-STRING>
             <ATTRIBUTE-DEFINITION-STRING IDENTIFIER="ReqIF.ChapterName" LONG-NAME="ReqIF.ChapterName">
               <TYPE>
                 <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
diff --git a/tests/end2end/project_index/import_document_from_reqif/UC55_T01_default_import/test_UC55_T01_default_import.py b/tests/end2end/project_index/import_document_from_reqif/import_document_default_import/test_case.py
similarity index 100%
rename from tests/end2end/project_index/import_document_from_reqif/UC55_T01_default_import/test_UC55_T01_default_import.py
rename to tests/end2end/project_index/import_document_from_reqif/import_document_default_import/test_case.py
diff --git a/tests/end2end/project_index/import_document_from_reqif/import_document_from_reqif_tree_of_two_documents/sample.reqif b/tests/end2end/project_index/import_document_from_reqif/import_document_from_reqif_tree_of_two_documents/sample.reqif
index 778cc119a..041086e97 100644
--- a/tests/end2end/project_index/import_document_from_reqif/import_document_from_reqif_tree_of_two_documents/sample.reqif
+++ b/tests/end2end/project_index/import_document_from_reqif/import_document_from_reqif_tree_of_two_documents/sample.reqif
@@ -37,11 +37,6 @@
                 <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
               </TYPE>
             </ATTRIBUTE-DEFINITION-STRING>
-            <ATTRIBUTE-DEFINITION-STRING IDENTIFIER="REFS" LONG-NAME="REFS">
-              <TYPE>
-                <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
-              </TYPE>
-            </ATTRIBUTE-DEFINITION-STRING>
             <ATTRIBUTE-DEFINITION-STRING IDENTIFIER="ReqIF.Name" LONG-NAME="ReqIF.Name">
               <TYPE>
                 <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
@@ -62,6 +57,11 @@
                 <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
               </TYPE>
             </ATTRIBUTE-DEFINITION-STRING>
+            <ATTRIBUTE-DEFINITION-STRING IDENTIFIER="REFS" LONG-NAME="REFS">
+              <TYPE>
+                <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
+              </TYPE>
+            </ATTRIBUTE-DEFINITION-STRING>
             <ATTRIBUTE-DEFINITION-STRING IDENTIFIER="ReqIF.ChapterName" LONG-NAME="ReqIF.ChapterName">
               <TYPE>
                 <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
@@ -93,11 +93,6 @@
                 <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
               </TYPE>
             </ATTRIBUTE-DEFINITION-STRING>
-            <ATTRIBUTE-DEFINITION-STRING IDENTIFIER="REFS" LONG-NAME="REFS">
-              <TYPE>
-                <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
-              </TYPE>
-            </ATTRIBUTE-DEFINITION-STRING>
             <ATTRIBUTE-DEFINITION-STRING IDENTIFIER="ReqIF.Name" LONG-NAME="ReqIF.Name">
               <TYPE>
                 <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
@@ -118,6 +113,11 @@
                 <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
               </TYPE>
             </ATTRIBUTE-DEFINITION-STRING>
+            <ATTRIBUTE-DEFINITION-STRING IDENTIFIER="REFS" LONG-NAME="REFS">
+              <TYPE>
+                <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
+              </TYPE>
+            </ATTRIBUTE-DEFINITION-STRING>
             <ATTRIBUTE-DEFINITION-STRING IDENTIFIER="ReqIF.ChapterName" LONG-NAME="ReqIF.ChapterName">
               <TYPE>
                 <DATATYPE-DEFINITION-STRING-REF>SDOC_DATATYPE_SINGLE_LINE_STRING</DATATYPE-DEFINITION-STRING-REF>
diff --git a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_field_move_up_and_down_save/expected_output/document.sdoc b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_field_move_up_and_down_save/expected_output/document.sdoc
index 8f6d17de5..4e7e422bb 100644
--- a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_field_move_up_and_down_save/expected_output/document.sdoc
+++ b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_field_move_up_and_down_save/expected_output/document.sdoc
@@ -17,9 +17,6 @@ ELEMENTS:
   - TITLE: TAGS
     TYPE: String
     REQUIRED: False
-  - TITLE: REFS
-    TYPE: String
-    REQUIRED: False
   - TITLE: TITLE
     TYPE: String
     REQUIRED: False
@@ -35,6 +32,8 @@ ELEMENTS:
   - TITLE: COMMENT
     TYPE: String
     REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
 
 [FREETEXT]
 Hello world!
diff --git a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_field_move_up_save/expected_output/document.sdoc b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_field_move_up_save/expected_output/document.sdoc
index f0552dc8c..71a3256c8 100644
--- a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_field_move_up_save/expected_output/document.sdoc
+++ b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_field_move_up_save/expected_output/document.sdoc
@@ -17,9 +17,6 @@ ELEMENTS:
   - TITLE: TAGS
     TYPE: String
     REQUIRED: False
-  - TITLE: REFS
-    TYPE: String
-    REQUIRED: False
   - TITLE: TITLE
     TYPE: String
     REQUIRED: False
@@ -35,6 +32,8 @@ ELEMENTS:
   - TITLE: COMMENT
     TYPE: String
     REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
 
 [FREETEXT]
 Hello world!
diff --git a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_new_field/__init__.py b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_new_field/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_field/expected_output/document.sdoc b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_new_field/expected_output/document.sdoc
similarity index 92%
rename from tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_field/expected_output/document.sdoc
rename to tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_new_field/expected_output/document.sdoc
index 048f0cc75..e831cbf54 100644
--- a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_field/expected_output/document.sdoc
+++ b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_new_field/expected_output/document.sdoc
@@ -17,9 +17,6 @@ ELEMENTS:
   - TITLE: TAGS
     TYPE: String
     REQUIRED: False
-  - TITLE: REFS
-    TYPE: String
-    REQUIRED: False
   - TITLE: TITLE
     TYPE: String
     REQUIRED: False
@@ -35,6 +32,8 @@ ELEMENTS:
   - TITLE: CUSTOM_FIELD
     TYPE: String
     REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
 
 [FREETEXT]
 Hello world!
diff --git a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_field/input/document.sdoc b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_new_field/input/document.sdoc
similarity index 100%
rename from tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_field/input/document.sdoc
rename to tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_new_field/input/document.sdoc
diff --git a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_field/test_case.py b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_new_field/test_case.py
similarity index 100%
rename from tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_field/test_case.py
rename to tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_new_field/test_case.py
diff --git a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_three_fields/expected_output/document.sdoc b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_three_fields/expected_output/document.sdoc
index d0b60844e..0a42e0c0f 100644
--- a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_three_fields/expected_output/document.sdoc
+++ b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_add_three_fields/expected_output/document.sdoc
@@ -17,9 +17,6 @@ ELEMENTS:
   - TITLE: TAGS
     TYPE: String
     REQUIRED: False
-  - TITLE: REFS
-    TYPE: String
-    REQUIRED: False
   - TITLE: TITLE
     TYPE: String
     REQUIRED: False
@@ -41,6 +38,8 @@ ELEMENTS:
   - TITLE: CUSTOM_FIELD_3
     TYPE: String
     REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
 
 [FREETEXT]
 Hello world!
diff --git a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_delete_existing_field/expected_output/document.sdoc b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_delete_existing_field/expected_output/document.sdoc
index ec14b5d5b..dc9a06022 100644
--- a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_delete_existing_field/expected_output/document.sdoc
+++ b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_delete_existing_field/expected_output/document.sdoc
@@ -14,9 +14,6 @@ ELEMENTS:
   - TITLE: TAGS
     TYPE: String
     REQUIRED: False
-  - TITLE: REFS
-    TYPE: String
-    REQUIRED: False
   - TITLE: TITLE
     TYPE: String
     REQUIRED: False
@@ -29,6 +26,8 @@ ELEMENTS:
   - TITLE: COMMENT
     TYPE: String
     REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
 
 [FREETEXT]
 Hello world!
diff --git a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_move_field_down/expected_output/document.sdoc b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_move_field_down/expected_output/document.sdoc
index 048f0cc75..e831cbf54 100644
--- a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_move_field_down/expected_output/document.sdoc
+++ b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_move_field_down/expected_output/document.sdoc
@@ -17,9 +17,6 @@ ELEMENTS:
   - TITLE: TAGS
     TYPE: String
     REQUIRED: False
-  - TITLE: REFS
-    TYPE: String
-    REQUIRED: False
   - TITLE: TITLE
     TYPE: String
     REQUIRED: False
@@ -35,6 +32,8 @@ ELEMENTS:
   - TITLE: CUSTOM_FIELD
     TYPE: String
     REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
 
 [FREETEXT]
 Hello world!
diff --git a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_move_field_up/expected_output/document.sdoc b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_move_field_up/expected_output/document.sdoc
index 8f6d17de5..4e7e422bb 100644
--- a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_move_field_up/expected_output/document.sdoc
+++ b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_move_field_up/expected_output/document.sdoc
@@ -17,9 +17,6 @@ ELEMENTS:
   - TITLE: TAGS
     TYPE: String
     REQUIRED: False
-  - TITLE: REFS
-    TYPE: String
-    REQUIRED: False
   - TITLE: TITLE
     TYPE: String
     REQUIRED: False
@@ -35,6 +32,8 @@ ELEMENTS:
   - TITLE: COMMENT
     TYPE: String
     REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
 
 [FREETEXT]
 Hello world!
diff --git a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_rename_field/expected_output/document.sdoc b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_rename_field/expected_output/document.sdoc
index 405363392..0caa338e6 100644
--- a/tests/end2end/screens/document/edit_document_grammar/edit_grammar_rename_field/expected_output/document.sdoc
+++ b/tests/end2end/screens/document/edit_document_grammar/edit_grammar_rename_field/expected_output/document.sdoc
@@ -17,6 +17,8 @@ ELEMENTS:
   - TITLE: CUSTOM_FIELD_2
     TYPE: String
     REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
 
 [FREETEXT]
 Hello world!
diff --git a/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T01_add_one_link/expected_output/document.sdoc b/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T01_add_one_link/expected_output/document.sdoc
index 025936722..f763d8f92 100644
--- a/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T01_add_one_link/expected_output/document.sdoc
+++ b/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T01_add_one_link/expected_output/document.sdoc
@@ -14,10 +14,10 @@ Requirement statement #1.
 
 [REQUIREMENT]
 UID: REQ-002
-REFS:
-- TYPE: Parent
-  VALUE: REQ-001
 TITLE: Requirement title #2
 STATEMENT: >>>
 Requirement statement #2.
 <<<
+REFS:
+- TYPE: Parent
+  VALUE: REQ-001
diff --git a/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T02_add_three_links/expected_output/document.sdoc b/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T02_add_three_links/expected_output/document.sdoc
index 301ac507a..21e83a27a 100644
--- a/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T02_add_three_links/expected_output/document.sdoc
+++ b/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T02_add_three_links/expected_output/document.sdoc
@@ -7,6 +7,10 @@ Hello world!
 
 [REQUIREMENT]
 UID: REQ-001
+TITLE: Requirement title #1
+STATEMENT: >>>
+Requirement statement #1.
+<<<
 REFS:
 - TYPE: Parent
   VALUE: REQ-002
@@ -14,10 +18,6 @@ REFS:
   VALUE: REQ-003
 - TYPE: Parent
   VALUE: REQ-004
-TITLE: Requirement title #1
-STATEMENT: >>>
-Requirement statement #1.
-<<<
 
 [REQUIREMENT]
 UID: REQ-002
diff --git a/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T14_renaming_uid_when_child_links_exist/expected_output/document.sdoc b/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T14_renaming_uid_when_child_links_exist/expected_output/document.sdoc
index 025936722..f763d8f92 100644
--- a/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T14_renaming_uid_when_child_links_exist/expected_output/document.sdoc
+++ b/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T14_renaming_uid_when_child_links_exist/expected_output/document.sdoc
@@ -14,10 +14,10 @@ Requirement statement #1.
 
 [REQUIREMENT]
 UID: REQ-002
-REFS:
-- TYPE: Parent
-  VALUE: REQ-001
 TITLE: Requirement title #2
 STATEMENT: >>>
 Requirement statement #2.
 <<<
+REFS:
+- TYPE: Parent
+  VALUE: REQ-001
diff --git a/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T14_renaming_uid_when_child_links_exist/input/document.sdoc b/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T14_renaming_uid_when_child_links_exist/input/document.sdoc
index 025936722..f763d8f92 100644
--- a/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T14_renaming_uid_when_child_links_exist/input/document.sdoc
+++ b/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T14_renaming_uid_when_child_links_exist/input/document.sdoc
@@ -14,10 +14,10 @@ Requirement statement #1.
 
 [REQUIREMENT]
 UID: REQ-002
-REFS:
-- TYPE: Parent
-  VALUE: REQ-001
 TITLE: Requirement title #2
 STATEMENT: >>>
 Requirement statement #2.
 <<<
+REFS:
+- TYPE: Parent
+  VALUE: REQ-001
diff --git a/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T20_two_documents_removing_link/input/document2.sdoc b/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T20_two_documents_removing_link/input/document2.sdoc
index d69a4b8f0..36c97ef25 100644
--- a/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T20_two_documents_removing_link/input/document2.sdoc
+++ b/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/UC07_G1_T20_two_documents_removing_link/input/document2.sdoc
@@ -7,10 +7,10 @@ Hello world 2!
 
 [REQUIREMENT]
 UID: REQ-002
-REFS:
-- TYPE: Parent
-  VALUE: REQ-001
 TITLE: Requirement title #2
 STATEMENT: >>>
 Requirement statement #2.
 <<<
+REFS:
+- TYPE: Parent
+  VALUE: REQ-001
diff --git a/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/update_requirement_remove_existing_link/input/document.sdoc b/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/update_requirement_remove_existing_link/input/document.sdoc
index 025936722..f763d8f92 100644
--- a/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/update_requirement_remove_existing_link/input/document.sdoc
+++ b/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/update_requirement_remove_existing_link/input/document.sdoc
@@ -14,10 +14,10 @@ Requirement statement #1.
 
 [REQUIREMENT]
 UID: REQ-002
-REFS:
-- TYPE: Parent
-  VALUE: REQ-001
 TITLE: Requirement title #2
 STATEMENT: >>>
 Requirement statement #2.
 <<<
+REFS:
+- TYPE: Parent
+  VALUE: REQ-001
diff --git a/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/update_requirement_renaming_uid_when_parent_links_exist/expected_output/document.sdoc b/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/update_requirement_renaming_uid_when_parent_links_exist/expected_output/document.sdoc
index 025936722..f763d8f92 100644
--- a/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/update_requirement_renaming_uid_when_parent_links_exist/expected_output/document.sdoc
+++ b/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/update_requirement_renaming_uid_when_parent_links_exist/expected_output/document.sdoc
@@ -14,10 +14,10 @@ Requirement statement #1.
 
 [REQUIREMENT]
 UID: REQ-002
-REFS:
-- TYPE: Parent
-  VALUE: REQ-001
 TITLE: Requirement title #2
 STATEMENT: >>>
 Requirement statement #2.
 <<<
+REFS:
+- TYPE: Parent
+  VALUE: REQ-001
diff --git a/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/update_requirement_renaming_uid_when_parent_links_exist/input/document.sdoc b/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/update_requirement_renaming_uid_when_parent_links_exist/input/document.sdoc
index 025936722..f763d8f92 100644
--- a/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/update_requirement_renaming_uid_when_parent_links_exist/input/document.sdoc
+++ b/tests/end2end/screens/document/edit_requirement/UC07_G1_editing_requirement_links/update_requirement_renaming_uid_when_parent_links_exist/input/document.sdoc
@@ -14,10 +14,10 @@ Requirement statement #1.
 
 [REQUIREMENT]
 UID: REQ-002
-REFS:
-- TYPE: Parent
-  VALUE: REQ-001
 TITLE: Requirement title #2
 STATEMENT: >>>
 Requirement statement #2.
 <<<
+REFS:
+- TYPE: Parent
+  VALUE: REQ-001
diff --git a/tests/integration/backend/excel/import/01_import_basic_e2e/expected/expected.sdoc b/tests/integration/backend/excel/import/01_import_basic_e2e/expected/expected.sdoc
index d07156b11..be603e0c3 100644
--- a/tests/integration/backend/excel/import/01_import_basic_e2e/expected/expected.sdoc
+++ b/tests/integration/backend/excel/import/01_import_basic_e2e/expected/expected.sdoc
@@ -17,9 +17,6 @@ ELEMENTS:
   - TITLE: TAGS
     TYPE: String
     REQUIRED: False
-  - TITLE: REFS
-    TYPE: Reference(ParentReqReference, ChildReqReference, FileReference, BibReference)
-    REQUIRED: False
   - TITLE: TITLE
     TYPE: String
     REQUIRED: False
@@ -47,6 +44,10 @@ ELEMENTS:
   - TITLE: CRITICALITY
     TYPE: String
     REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
+  - TYPE: Child
+  - TYPE: File
 
 [REQUIREMENT]
 UID: A-1
diff --git a/tests/integration/backend/reqif/profiles/p01_sdoc/end_to_end/13_refs/sample.sdoc b/tests/integration/backend/reqif/profiles/p01_sdoc/end_to_end/13_refs/sample.sdoc
index d3e2f5afe..73b3248af 100644
--- a/tests/integration/backend/reqif/profiles/p01_sdoc/end_to_end/13_refs/sample.sdoc
+++ b/tests/integration/backend/reqif/profiles/p01_sdoc/end_to_end/13_refs/sample.sdoc
@@ -7,7 +7,7 @@ TITLE: Requirement #1
 
 [REQUIREMENT]
 UID: REQ-002
+TITLE: Requirement #2
 REFS:
 - TYPE: Parent
   VALUE: REQ-001
-TITLE: Requirement #2
diff --git a/tests/integration/backend/reqif/profiles/p01_sdoc/end_to_end/30_custom_grammar/sample.sdoc b/tests/integration/backend/reqif/profiles/p01_sdoc/end_to_end/30_custom_grammar/sample.sdoc
index c788f7984..0bf3137ff 100644
--- a/tests/integration/backend/reqif/profiles/p01_sdoc/end_to_end/30_custom_grammar/sample.sdoc
+++ b/tests/integration/backend/reqif/profiles/p01_sdoc/end_to_end/30_custom_grammar/sample.sdoc
@@ -20,6 +20,8 @@ ELEMENTS:
   - TITLE: COMMENT
     TYPE: String
     REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
 
 [REQUIREMENT]
 UID: ABC-123
diff --git a/tests/integration/backend/reqif/profiles/p01_sdoc/end_to_end/31_custom_grammar_single_choice_type/sample.sdoc b/tests/integration/backend/reqif/profiles/p01_sdoc/end_to_end/31_custom_grammar_single_choice_type/sample.sdoc
index 0e7246e91..44531c75a 100644
--- a/tests/integration/backend/reqif/profiles/p01_sdoc/end_to_end/31_custom_grammar_single_choice_type/sample.sdoc
+++ b/tests/integration/backend/reqif/profiles/p01_sdoc/end_to_end/31_custom_grammar_single_choice_type/sample.sdoc
@@ -11,6 +11,8 @@ ELEMENTS:
   - TITLE: STATEMENT
     TYPE: String
     REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
 
 [REQUIREMENT]
 CHOICE_FIELD: A
diff --git a/tests/integration/backend/reqif/profiles/p01_sdoc/end_to_end/32_custom_grammar_multi_choice_type/sample.sdoc b/tests/integration/backend/reqif/profiles/p01_sdoc/end_to_end/32_custom_grammar_multi_choice_type/sample.sdoc
index 95d7c1402..8aba554b0 100644
--- a/tests/integration/backend/reqif/profiles/p01_sdoc/end_to_end/32_custom_grammar_multi_choice_type/sample.sdoc
+++ b/tests/integration/backend/reqif/profiles/p01_sdoc/end_to_end/32_custom_grammar_multi_choice_type/sample.sdoc
@@ -11,6 +11,8 @@ ELEMENTS:
   - TITLE: STATEMENT
     TYPE: String
     REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
 
 [REQUIREMENT]
 CHOICE_FIELD: A, B
diff --git a/tests/integration/scripting_examples/reqif/02_user_provided_example/script.py b/tests/integration/scripting_examples/reqif/02_user_provided_example/script.py
index 61235271d..610977322 100644
--- a/tests/integration/scripting_examples/reqif/02_user_provided_example/script.py
+++ b/tests/integration/scripting_examples/reqif/02_user_provided_example/script.py
@@ -350,7 +350,7 @@ def create_grammar_element_from_spec_object_type(
             else:
                 raise NotImplementedError(attribute) from None
         requirement_element = GrammarElement(
-            parent=None, tag="REQUIREMENT", fields=fields
+            parent=None, tag="REQUIREMENT", fields=fields, relations=[]
         )
         return requirement_element
 
diff --git a/tests/unit/helpers/test_document_builder.py b/tests/unit/helpers/test_document_builder.py
index 6b83e667a..d4e228328 100644
--- a/tests/unit/helpers/test_document_builder.py
+++ b/tests/unit/helpers/test_document_builder.py
@@ -47,7 +47,7 @@ def add_requirement_parent(self, req_id, parent_req_id):
         assert requirement
 
         reference = ParentReqReference(
-            requirement, parent_req_id, relation_uid=None
+            requirement, parent_req_id, role_uid=None
         )
         requirement.references.append(reference)
 
diff --git a/tests/unit/strictdoc/backend/sdoc/test_dsl_passthrough.py b/tests/unit/strictdoc/backend/sdoc/test_dsl_passthrough.py
index 42546cb6a..dca954da8 100644
--- a/tests/unit/strictdoc/backend/sdoc/test_dsl_passthrough.py
+++ b/tests/unit/strictdoc/backend/sdoc/test_dsl_passthrough.py
@@ -1,14 +1,9 @@
-import re
-
 import pytest
 from textx import TextXSyntaxError
 
-from strictdoc.backend.sdoc.error_handling import StrictDocSemanticError
 from strictdoc.backend.sdoc.models.document import Document
 from strictdoc.backend.sdoc.models.reference import (
-    BibReference,
     FileReference,
-    ParentReqReference,
 )
 from strictdoc.backend.sdoc.models.requirement import (
     CompositeRequirement,
@@ -16,7 +11,6 @@
 )
 from strictdoc.backend.sdoc.models.section import Section
 from strictdoc.backend.sdoc.models.type_system import (
-    BibEntryFormat,
     ReferenceType,
 )
 from strictdoc.backend.sdoc.reader import SDReader
@@ -24,7 +18,7 @@
 
 
 def test_001_minimal_doc():
-    sdoc_input = """
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 
@@ -37,17 +31,17 @@ def test_001_minimal_doc():
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
+    document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
     writer = SDWriter()
     output = writer.write(document)
 
-    assert sdoc_input == output
+    assert input_sdoc == output
 
 
 def test_002_minimal_req():
-    sdoc_input = """
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 
@@ -57,17 +51,17 @@ def test_002_minimal_req():
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
+    document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
     writer = SDWriter()
     output = writer.write(document)
 
-    assert sdoc_input == output
+    assert input_sdoc == output
 
 
 def test_003_comments_01_several_comments():
-    sdoc_input = """
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 
@@ -80,17 +74,17 @@ def test_003_comments_01_several_comments():
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
+    document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
     writer = SDWriter()
     output = writer.write(document)
 
-    assert sdoc_input == output
+    assert input_sdoc == output
 
 
 def test_004_several_tags():
-    sdoc_input = """
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 
@@ -101,13 +95,13 @@ def test_004_several_tags():
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
+    document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
     writer = SDWriter()
     output = writer.write(document)
 
-    assert sdoc_input == output
+    assert input_sdoc == output
 
 
 def test_010_multiple_sections():
@@ -151,32 +145,6 @@ def test_010_multiple_sections():
     assert input_sdoc == output
 
 
-def test_020_parent_ref_with_relation():
-    input_sdoc = """
-[DOCUMENT]
-TITLE: Test Doc
-
-[REQUIREMENT]
-REFS:
-- TYPE: Parent
-  VALUE: ID-001
-  RELATION: Refines
-STATEMENT: >>>
-This is a statement.
-<<<
-""".lstrip()
-
-    reader = SDReader()
-
-    document = reader.read(input_sdoc)
-    assert isinstance(document, Document)
-
-    writer = SDWriter()
-    output = writer.write(document)
-
-    assert input_sdoc == output
-
-
 def test_030_multiline_statement():
     input_sdoc = """
 [DOCUMENT]
@@ -417,7 +385,7 @@ def test_042_composite_requirement_2_level():
 # This test is needed to make sure that the grammar details related
 # to the difference of parting single vs multiline strings are covered.
 def test_050_requirement_single_line_statement_one_symbol():
-    sdoc_input = """
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 
@@ -427,17 +395,17 @@ def test_050_requirement_single_line_statement_one_symbol():
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
+    document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
-    document: Document = reader.read(sdoc_input)
+    document: Document = reader.read(input_sdoc)
     requirement = document.section_contents[0]
     assert requirement.reserved_statement == "1"
 
     writer = SDWriter()
     output = writer.write(document)
 
-    assert sdoc_input == output
+    assert input_sdoc == output
 
 
 def test_060_file_ref():
@@ -472,7 +440,7 @@ def test_060_file_ref():
 
 
 def test_070_document_config_version():
-    input = """
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 VERSION: 0.0.1
@@ -485,20 +453,20 @@ def test_070_document_config_version():
 
     reader = SDReader()
 
-    document = reader.read(input)
+    document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
-    document: Document = reader.read(input)
+    document: Document = reader.read(input_sdoc)
     assert document.config.version == "0.0.1"
 
     writer = SDWriter()
     output = writer.write(document)
 
-    assert input == output
+    assert input_sdoc == output
 
 
 def test_071_document_config_number():
-    input = """
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 UID: SDOC-01
@@ -511,20 +479,20 @@ def test_071_document_config_number():
 
     reader = SDReader()
 
-    document = reader.read(input)
+    document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
-    document: Document = reader.read(input)
+    document: Document = reader.read(input_sdoc)
     assert document.config.uid == "SDOC-01"
 
     writer = SDWriter()
     output = writer.write(document)
 
-    assert input == output
+    assert input_sdoc == output
 
 
 def test_072_document_config_classification():
-    input = """
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 UID: SDOC-01
@@ -539,20 +507,20 @@ def test_072_document_config_classification():
 
     reader = SDReader()
 
-    document = reader.read(input)
+    document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
-    document: Document = reader.read(input)
+    document: Document = reader.read(input_sdoc)
     assert document.config.classification == "Restricted"
 
     writer = SDWriter()
     output = writer.write(document)
 
-    assert input == output
+    assert input_sdoc == output
 
 
 def test_073_document_config_requirement_prefix():
-    input = """
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 UID: SDOC-01
@@ -567,20 +535,20 @@ def test_073_document_config_requirement_prefix():
 
     reader = SDReader()
 
-    document = reader.read(input)
+    document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
-    document: Document = reader.read(input)
+    document: Document = reader.read(input_sdoc)
     assert document.config.requirement_prefix == "DOC-"
 
     writer = SDWriter()
     output = writer.write(document)
 
-    assert input == output
+    assert input_sdoc == output
 
 
 def test_090_document_config_all_fields():
-    input = """
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 UID: SDOC-01
@@ -605,10 +573,10 @@ def test_090_document_config_all_fields():
 
     reader = SDReader()
 
-    document = reader.read(input)
+    document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
-    document: Document = reader.read(input)
+    document: Document = reader.read(input_sdoc)
     assert document.title == "Test Doc"
     assert document.config.version == "0.0.1"
     assert document.config.uid == "SDOC-01"
@@ -629,7 +597,7 @@ def test_090_document_config_all_fields():
     writer = SDWriter()
     output = writer.write(document)
 
-    assert input == output
+    assert input_sdoc == output
 
 
 def test_100_basic_test():
@@ -642,6 +610,8 @@ def test_100_basic_test():
 
 [REQUIREMENT]
 TAGS: Tag 1, Tag 2, Tag 3
+STATEMENT: System shall do X
+COMMENT: This requirement is very important
 REFS:
 - TYPE: File
   VALUE: /usr/local/bin/hexe
@@ -649,8 +619,6 @@ def test_100_basic_test():
   VALUE: /usr/local/bin/hexe
 - TYPE: File
   VALUE: /usr/local/bin/hexe
-STATEMENT: System shall do X
-COMMENT: This requirement is very important
 
 [REQUIREMENT]
 UID: REQ-001
@@ -682,7 +650,7 @@ def test_100_basic_test():
 
 
 def test_081_document_config_markup_not_specified():
-    input = """
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 VERSION: 0.0.1
@@ -695,21 +663,21 @@ def test_081_document_config_markup_not_specified():
 
     reader = SDReader()
 
-    document = reader.read(input)
+    document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
-    document: Document = reader.read(input)
+    document: Document = reader.read(input_sdoc)
     assert document.config.version == "0.0.1"
     assert document.config.markup is None
 
     writer = SDWriter()
     output = writer.write(document)
 
-    assert input == output
+    assert input_sdoc == output
 
 
 def test_081_document_config_markup_specified():
-    input = """
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 VERSION: 0.0.1
@@ -724,20 +692,20 @@ def test_081_document_config_markup_specified():
 
     reader = SDReader()
 
-    document = reader.read(input)
+    document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
-    document: Document = reader.read(input)
+    document: Document = reader.read(input_sdoc)
     assert document.config.version == "0.0.1"
 
     writer = SDWriter()
     output = writer.write(document)
 
-    assert input == output
+    assert input_sdoc == output
 
 
 def test_082_document_config_auto_levels_specified_to_false():
-    sdoc_input = """
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 VERSION: 0.0.1
@@ -747,20 +715,20 @@ def test_082_document_config_auto_levels_specified_to_false():
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
+    document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
-    document: Document = reader.read(sdoc_input)
+    document: Document = reader.read(input_sdoc)
     assert document.config.auto_levels is False
 
     writer = SDWriter()
     output = writer.write(document)
 
-    assert sdoc_input == output
+    assert input_sdoc == output
 
 
 def test_083_requirement_level():
-    sdoc_input = """
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 VERSION: 0.0.1
@@ -780,10 +748,10 @@ def test_083_requirement_level():
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
+    document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
-    document: Document = reader.read(sdoc_input)
+    document: Document = reader.read(input_sdoc)
     assert document.config.auto_levels is False
     section: Section = document.section_contents[0]
     assert section.custom_level == "123"
@@ -795,11 +763,11 @@ def test_083_requirement_level():
     writer = SDWriter()
     output = writer.write(document)
 
-    assert sdoc_input == output
+    assert input_sdoc == output
 
 
 def test_085_options_requirement_style():
-    sdoc_input = """
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 VERSION: 0.0.1
@@ -809,20 +777,20 @@ def test_085_options_requirement_style():
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
+    document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
-    document: Document = reader.read(sdoc_input)
+    document: Document = reader.read(input_sdoc)
     assert document.config.requirement_style == "Table"
 
     writer = SDWriter()
     output = writer.write(document)
 
-    assert sdoc_input == output
+    assert input_sdoc == output
 
 
 def test_087_options_requirement_in_toc():
-    sdoc_input = """
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 VERSION: 0.0.1
@@ -832,972 +800,240 @@ def test_087_options_requirement_in_toc():
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
+    document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
-    document: Document = reader.read(sdoc_input)
+    document: Document = reader.read(input_sdoc)
     assert document.config.requirement_in_toc == "True"
 
     writer = SDWriter()
     output = writer.write(document)
 
-    assert sdoc_input == output
+    assert input_sdoc == output
 
 
-def test_150_grammar_minimal_doc():
-    sdoc_input = """
+def test_edge_case_01_minimal_requirement():
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 
-[GRAMMAR]
-ELEMENTS:
-- TAG: LOW_LEVEL_REQUIREMENT
-  FIELDS:
-  - TITLE: STATEMENT
-    TYPE: String
-    REQUIRED: True
+[REQUIREMENT]
 """.lstrip()
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
+    document: Document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
+    requirement: Requirement = document.section_contents[0]
+    assert requirement.reserved_uid is None
+    assert requirement.reserved_title is None
+    assert requirement.reserved_statement is None
+
     writer = SDWriter()
     output = writer.write(document)
 
-    assert sdoc_input == output
+    assert input_sdoc == output
 
 
-def test_151_grammar_single_choice():
-    sdoc_input = """
+def test_edge_case_02_uid_present_but_empty_with_no_space_character():
+    # Note: There is no whitespace character after "UID:".
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 
-[GRAMMAR]
-ELEMENTS:
-- TAG: LOW_LEVEL_REQUIREMENT
-  FIELDS:
-  - TITLE: SINGLE_CHOICE_FIELD
-    TYPE: SingleChoice(A, B, C)
-    REQUIRED: True
-  - TITLE: STATEMENT
-    TYPE: String
-    REQUIRED: False
-
-[LOW_LEVEL_REQUIREMENT]
-SINGLE_CHOICE_FIELD: A
+[REQUIREMENT]
+UID:
 """.lstrip()
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
-    assert isinstance(document, Document)
-
-    writer = SDWriter()
-    output = writer.write(document)
+    with pytest.raises(Exception) as exc_info:
+        _ = reader.read(input_sdoc)
 
-    assert sdoc_input == output
+    assert exc_info.type is TextXSyntaxError
+    assert "Expected ' '" == exc_info.value.args[0].decode("utf-8")
 
 
-def test_152_grammar_multiple_choice():
-    sdoc_input = """
+def test_edge_case_03_uid_present_but_empty_with_space_character():
+    # Note: There is a whitespace character after "UID:".
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 
-[GRAMMAR]
-ELEMENTS:
-- TAG: LOW_LEVEL_REQUIREMENT
-  FIELDS:
-  - TITLE: MULTIPLE_CHOICE_FIELD
-    TYPE: MultipleChoice(A, B, C)
-    REQUIRED: True
-  - TITLE: STATEMENT
-    TYPE: String
-    REQUIRED: False
-
-[LOW_LEVEL_REQUIREMENT]
-MULTIPLE_CHOICE_FIELD: A, C
-""".lstrip()
+[REQUIREMENT]
+UID: 
+""".lstrip()  # noqa: W291
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
-    assert isinstance(document, Document)
-
-    writer = SDWriter()
-    output = writer.write(document)
+    with pytest.raises(Exception) as exc_info:
+        _ = reader.read(input_sdoc)
 
-    assert sdoc_input == output
+    assert exc_info.type is TextXSyntaxError
+    assert "Expected SingleLineString or '>>>\\n'" in exc_info.value.args[
+        0
+    ].decode("utf-8")
 
 
-def test_153_grammar_tag():
-    sdoc_input = """
+def test_edge_case_04_uid_present_but_empty_with_two_space_characters():
+    # Note: There are two whitespace characters after "UID:".
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 
-[GRAMMAR]
-ELEMENTS:
-- TAG: LOW_LEVEL_REQUIREMENT
-  FIELDS:
-  - TITLE: TAG_FIELD
-    TYPE: Tag
-    REQUIRED: True
-  - TITLE: STATEMENT
-    TYPE: String
-    REQUIRED: False
-
-[LOW_LEVEL_REQUIREMENT]
-TAG_FIELD: A, C
-""".lstrip()
+[REQUIREMENT]
+UID:  
+""".lstrip()  # noqa: W291
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
-    assert isinstance(document, Document)
-
-    writer = SDWriter()
-    output = writer.write(document)
+    with pytest.raises(Exception) as exc_info:
+        _ = reader.read(input_sdoc)
 
-    assert sdoc_input == output
+    assert exc_info.type is TextXSyntaxError
+    assert "Expected SingleLineString or '>>>\\n'" in exc_info.value.args[
+        0
+    ].decode("utf-8")
 
 
-def test_154_grammar_multiline_custom_field():
-    sdoc_input = """
+def test_edge_case_10_empty_multiline_field():
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 
-[GRAMMAR]
-ELEMENTS:
-- TAG: REQUIREMENT
-  FIELDS:
-  - TITLE: MY_FIELD
-    TYPE: String
-    REQUIRED: True
-  - TITLE: STATEMENT
-    TYPE: String
-    REQUIRED: False
-
 [REQUIREMENT]
-MY_FIELD: >>>
-Some text here...
-Some text here...
-Some text here...
+COMMENT: >>>
 <<<
 """.lstrip()
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
-    assert isinstance(document, Document)
-
-    writer = SDWriter()
-    output = writer.write(document)
+    with pytest.raises(Exception) as exc_info:
+        _ = reader.read(input_sdoc)
 
-    assert sdoc_input == output
+    assert exc_info.type is TextXSyntaxError
+    assert (
+        "Expected '(?ms)(?!^<<<) *(?!^<<<)\\S((?!^<<<).)+'"
+        in exc_info.value.args[0].decode("utf-8")
+    )
 
 
-def test_160_grammar_refs():
-    sdoc_input = """
+def test_edge_case_11_empty_multiline_field_with_one_newline():
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 
-[GRAMMAR]
-ELEMENTS:
-- TAG: LOW_LEVEL_REQUIREMENT
-  FIELDS:
-  - TITLE: UID
-    TYPE: String
-    REQUIRED: True
-  - TITLE: REFS
-    TYPE: Reference(ParentReqReference, FileReference, BibReference)
-    REQUIRED: False
-  - TITLE: STATEMENT
-    TYPE: String
-    REQUIRED: False
-
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-000
+[REQUIREMENT]
+COMMENT: >>>
 
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-001
-REFS:
-- TYPE: File
-  VALUE: /tmp/sample0.cpp
-- TYPE: Parent
-  VALUE: ID-000
-- TYPE: BibRef
-  FORMAT: BibTex
-  VALUE: @book{hawking1989brief, title={A Brief History of Time: From the Big Bang to Black Holes}, author={Hawking, Stephen}, isbn={9780553176988}, year={1989}, publisher={Bantam Books} }
-
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-002
-REFS:
-- TYPE: Parent
-  VALUE: ID-001
-- TYPE: File
-  VALUE: /tmp/sample1.cpp
-- TYPE: File
-  VALUE: /tmp/sample2.cpp
-- TYPE: BibRef
-  FORMAT: String
-  VALUE: SampleCiteKeyStringRef-1, "The sample BibReference String-Format"
-""".lstrip()  # noqa: E501
+<<<
+""".lstrip()
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
-    assert isinstance(document, Document)
-
-    ll_requirement = document.section_contents[2]
-    references = ll_requirement.references
-    assert len(references) == 4
-
-    reference = references[0]
-    assert isinstance(reference, ParentReqReference)
-    assert reference.ref_type == ReferenceType.PARENT
-    assert reference.ref_uid == "ID-001"
-
-    reference: FileReference = references[1]
-    assert reference.ref_type == ReferenceType.FILE
-    assert isinstance(reference, FileReference)
-    assert reference.g_file_entry.g_file_path == "/tmp/sample1.cpp"
-
-    reference = references[2]
-    assert reference.ref_type == ReferenceType.FILE
-    assert isinstance(reference, FileReference)
-    assert reference.g_file_entry.g_file_path == "/tmp/sample2.cpp"
+    with pytest.raises(Exception) as exc_info:
+        _ = reader.read(input_sdoc)
 
-    reference = references[3]
-    assert reference.ref_type == ReferenceType.BIB_REF
-    assert isinstance(reference, BibReference)
+    assert exc_info.type is TextXSyntaxError
     assert (
-        reference.bib_entry.bib_value == "SampleCiteKeyStringRef-1, "
-        '"The sample BibReference String-Format"'
+        "Expected '(?ms)(?!^<<<) *(?!^<<<)\\S((?!^<<<).)+'"
+        in exc_info.value.args[0].decode("utf-8")
     )
 
-    writer = SDWriter()
-    output = writer.write(document)
-
-    assert sdoc_input == output
 
-
-def test_161_grammar_refs_file():
-    sdoc_input = """
+def test_edge_case_20_empty_section_title():
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 
-[GRAMMAR]
-ELEMENTS:
-- TAG: LOW_LEVEL_REQUIREMENT
-  FIELDS:
-  - TITLE: REFS
-    TYPE: Reference(ParentReqReference, FileReference, BibReference)
-    REQUIRED: False
-  - TITLE: STATEMENT
-    TYPE: String
-    REQUIRED: False
+[SECTION]
+TITLE:
 
-[LOW_LEVEL_REQUIREMENT]
-REFS:
-- TYPE: File
-  VALUE: /tmp/sample.cpp
+[/SECTION]
 """.lstrip()
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
-    assert isinstance(document, Document)
-
-    ll_requirement = document.section_contents[0]
-    references = ll_requirement.references
-    assert len(references) == 1
-
-    reference: FileReference = references[0]
-    assert isinstance(reference, FileReference)
-    assert reference.ref_type == ReferenceType.FILE
-    assert reference.g_file_entry.g_file_path == "/tmp/sample.cpp"
-
-    writer = SDWriter()
-    output = writer.write(document)
+    with pytest.raises(Exception) as exc_info:
+        _ = reader.read(input_sdoc)
 
-    assert sdoc_input == output
+    assert exc_info.type is TextXSyntaxError
+    assert "Expected 'UID: ' or 'LEVEL: ' or 'TITLE: '" == exc_info.value.args[
+        0
+    ].decode("utf-8")
 
 
-def test_162_grammar_refs_file_multi():
-    sdoc_input = """
+def test_edge_case_21_section_title_with_empty_space():
+    # Empty space after TITLE:
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 
-[GRAMMAR]
-ELEMENTS:
-- TAG: LOW_LEVEL_REQUIREMENT
-  FIELDS:
-  - TITLE: REFS
-    TYPE: Reference(ParentReqReference, FileReference, BibReference)
-    REQUIRED: False
-  - TITLE: STATEMENT
-    TYPE: String
-    REQUIRED: False
+[SECTION]
+TITLE: 
 
-[LOW_LEVEL_REQUIREMENT]
-REFS:
-- TYPE: File
-  VALUE: /tmp/sample1.cpp
-- TYPE: File
-  VALUE: /tmp/sample2.cpp
-- TYPE: File
-  VALUE: /tmp/sample3.cpp
-""".lstrip()
+[/SECTION]
+""".lstrip()  # noqa: W291
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
-    assert isinstance(document, Document)
-
-    ll_requirement = document.section_contents[0]
-    references = ll_requirement.references
-    assert len(references) == 3
-
-    reference: FileReference = references[0]
-    assert isinstance(reference, FileReference)
-    assert reference.ref_type == ReferenceType.FILE
-    assert reference.g_file_entry.g_file_path == "/tmp/sample1.cpp"
-
-    reference = references[1]
-    assert isinstance(reference, FileReference)
-    assert reference.ref_type == ReferenceType.FILE
-    assert reference.g_file_entry.g_file_path == "/tmp/sample2.cpp"
-
-    reference = references[2]
-    assert isinstance(reference, FileReference)
-    assert reference.ref_type == ReferenceType.FILE
-    assert reference.g_file_entry.g_file_path == "/tmp/sample3.cpp"
-
-    writer = SDWriter()
-    output = writer.write(document)
-
-    assert sdoc_input == output
-
-
-def test_163_grammar_refs_file_only():
-    sdoc_input = """
-[DOCUMENT]
-TITLE: Test Doc
-
-[GRAMMAR]
-ELEMENTS:
-- TAG: LOW_LEVEL_REQUIREMENT
-  FIELDS:
-  - TITLE: UID
-    TYPE: String
-    REQUIRED: True
-  - TITLE: REFS
-    TYPE: Reference(FileReference)
-    REQUIRED: False
-  - TITLE: STATEMENT
-    TYPE: String
-    REQUIRED: False
-
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-001
-
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-002
-REFS:
-- TYPE: Parent
-  VALUE: ID-001
-- TYPE: File
-  VALUE: /tmp/sample1.cpp
-""".lstrip()
-
-    reader = SDReader()
     with pytest.raises(Exception) as exc_info:
-        _ = reader.read(sdoc_input)
-
-    assert exc_info.type is StrictDocSemanticError
-    assert re.fullmatch(
-        "Requirement field of type Reference has an unsupported Reference "
-        'Type item: ParentReqReference\\(.*ref_uid = "ID-001".*\\).',
-        exc_info.value.args[0],
-    )
-
-
-def test_164_grammar_refs_parent():
-    sdoc_input = """
-[DOCUMENT]
-TITLE: Test Doc
-
-[GRAMMAR]
-ELEMENTS:
-- TAG: LOW_LEVEL_REQUIREMENT
-  FIELDS:
-  - TITLE: UID
-    TYPE: String
-    REQUIRED: True
-  - TITLE: REFS
-    TYPE: Reference(ParentReqReference, FileReference, BibReference)
-    REQUIRED: False
-  - TITLE: STATEMENT
-    TYPE: String
-    REQUIRED: False
+        _ = reader.read(input_sdoc)
 
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-000
-
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-001
-REFS:
-- TYPE: File
-  VALUE: /tmp/sample0.cpp
-- TYPE: Parent
-  VALUE: ID-000
-
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-002
-REFS:
-- TYPE: Parent
-  VALUE: ID-001
-""".lstrip()
-
-    reader = SDReader()
-
-    document = reader.read(sdoc_input)
-    assert isinstance(document, Document)
-
-    ll_requirement = document.section_contents[2]
-    references = ll_requirement.references
-    assert len(references) == 1
-
-    reference = references[0]
-    assert isinstance(reference, ParentReqReference)
-    assert reference.ref_type == ReferenceType.PARENT
-    assert reference.ref_uid == "ID-001"
-
-    writer = SDWriter()
-    output = writer.write(document)
-
-    assert sdoc_input == output
+    assert exc_info.type is TextXSyntaxError
+    assert "Expected SingleLineString" in exc_info.value.args[0].decode("utf-8")
 
 
-def test_165_grammar_refs_parent_multi():
-    sdoc_input = """
+def test_edge_case_22_section_title_with_two_empty_spaces():
+    # Two empty spaces after TITLE:
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 
-[GRAMMAR]
-ELEMENTS:
-- TAG: LOW_LEVEL_REQUIREMENT
-  FIELDS:
-  - TITLE: UID
-    TYPE: String
-    REQUIRED: True
-  - TITLE: REFS
-    TYPE: Reference(ParentReqReference, FileReference, BibReference)
-    REQUIRED: False
-  - TITLE: STATEMENT
-    TYPE: String
-    REQUIRED: False
-
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-000
-
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-001
+[SECTION]
+TITLE:  
 
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-002
-REFS:
-- TYPE: Parent
-  VALUE: ID-000
-- TYPE: Parent
-  VALUE: ID-001
-""".lstrip()
+[/SECTION]
+""".lstrip()  # noqa: W291
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
-    assert isinstance(document, Document)
-
-    ll_requirement = document.section_contents[2]
-    references = ll_requirement.references
-    assert len(references) == 2
-
-    reference = references[0]
-    assert isinstance(reference, ParentReqReference)
-    assert reference.ref_type == ReferenceType.PARENT
-    assert reference.ref_uid == "ID-000"
-
-    reference = references[1]
-    assert isinstance(reference, ParentReqReference)
-    assert reference.ref_type == ReferenceType.PARENT
-    assert reference.ref_uid == "ID-001"
-
-    writer = SDWriter()
-    output = writer.write(document)
-
-    assert sdoc_input == output
-
-
-def test_166_grammar_refs_parent_only():
-    sdoc_input = """
-[DOCUMENT]
-TITLE: Test Doc
-
-[GRAMMAR]
-ELEMENTS:
-- TAG: LOW_LEVEL_REQUIREMENT
-  FIELDS:
-  - TITLE: UID
-    TYPE: String
-    REQUIRED: True
-  - TITLE: REFS
-    TYPE: Reference(ParentReqReference)
-    REQUIRED: False
-  - TITLE: STATEMENT
-    TYPE: String
-    REQUIRED: False
-
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-001
-
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-002
-REFS:
-- TYPE: Parent
-  VALUE: ID-001
-- TYPE: File
-  VALUE: /tmp/sample1.cpp
-""".lstrip()
-
-    reader = SDReader()
     with pytest.raises(Exception) as exc_info:
-        _ = reader.read(sdoc_input)
-
-    assert exc_info.type is StrictDocSemanticError
-
-    assert re.fullmatch(
-        "Requirement field of type Reference has an unsupported Reference"
-        " Type item: FileReference\\(.*\\).",
-        exc_info.value.args[0],
-    )
-
-
-def test_167_grammar_refs_bib():
-    sdoc_input = """
-[DOCUMENT]
-TITLE: Test Doc
-
-[GRAMMAR]
-ELEMENTS:
-- TAG: LOW_LEVEL_REQUIREMENT
-  FIELDS:
-  - TITLE: UID
-    TYPE: String
-    REQUIRED: True
-  - TITLE: REFS
-    TYPE: Reference(ParentReqReference, FileReference, BibReference)
-    REQUIRED: False
-  - TITLE: STATEMENT
-    TYPE: String
-    REQUIRED: False
-
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-000
-
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-001
-REFS:
-- TYPE: File
-  VALUE: /tmp/sample0.cpp
-- TYPE: Parent
-  VALUE: ID-000
-- TYPE: BibRef
-  FORMAT: BibTex
-  VALUE: @book{hawking1989brief, title={A Brief History of Time: From the Big Bang to Black Holes}, author={Hawking, Stephen}, isbn={9780553176988}, year={1989}, publisher={Bantam Books} }
-
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-002
-REFS:
-- TYPE: Parent
-  VALUE: ID-001
-- TYPE: BibRef
-  FORMAT: String
-  VALUE: SampleCiteKeyStringRef-1, "The sample BibReference String-Format"
-- TYPE: BibRef
-  FORMAT: String
-  VALUE: SampleCiteKeyStringRef-2
-- TYPE: BibRef
-  FORMAT: Citation
-  VALUE: hawking1989brief, section 2.1
-""".lstrip()  # noqa: E501
-
-    reader = SDReader()
-
-    document = reader.read(sdoc_input)
-    assert isinstance(document, Document)
-
-    ll_requirement = document.section_contents[2]
-    references = ll_requirement.references
-    assert len(references) == 4
+        _ = reader.read(input_sdoc)
 
-    reference = references[1]
-    assert isinstance(reference, BibReference)
-    assert reference.ref_type == ReferenceType.BIB_REF
-    assert reference.bib_entry.bib_format == BibEntryFormat.STRING
-    assert (
-        reference.bib_entry.bib_value == "SampleCiteKeyStringRef-1,"
-        ' "The sample BibReference'
-        ' String-Format"'
-    )
-    assert reference.bib_entry.ref_cite == "SampleCiteKeyStringRef-1"
-    assert (
-        reference.bib_entry.ref_detail
-        == '"The sample BibReference String-Format"'
-    )
-    assert reference.bib_entry.bibtex_entry.type == "misc"
-    assert (
-        reference.bib_entry.bibtex_entry.fields["note"]
-        == '"The sample BibReference String-Format"'
-    )
-
-    reference = references[2]
-    assert isinstance(reference, BibReference)
-    assert reference.ref_type == ReferenceType.BIB_REF
-    assert reference.bib_entry.bib_format == BibEntryFormat.STRING
-    assert reference.bib_entry.bib_value == "SampleCiteKeyStringRef-2"
-    assert reference.bib_entry.ref_cite == "SampleCiteKeyStringRef-2"
-    assert reference.bib_entry.ref_detail is None
-    assert reference.bib_entry.bibtex_entry is None
-
-    reference = references[3]
-    assert isinstance(reference, BibReference)
-    assert reference.ref_type == ReferenceType.BIB_REF
-    assert reference.bib_entry.bib_format == BibEntryFormat.CITATION
-    assert reference.bib_entry.bib_value == "hawking1989brief, section 2.1"
-    assert reference.bib_entry.ref_cite == "hawking1989brief"
-    assert reference.bib_entry.ref_detail == "section 2.1"
-    assert reference.bib_entry.bibtex_entry is None
-
-    writer = SDWriter()
-    output = writer.write(document)
-
-    assert sdoc_input == output
+    assert exc_info.type is TextXSyntaxError
+    assert "Expected SingleLineString" in exc_info.value.args[0].decode("utf-8")
 
 
-def test_168_grammar_refs_bib_multi():
-    sdoc_input = """
+def test_edge_case_23_leading_spaces_do_not_imply_empy_field():
+    input_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 
 [GRAMMAR]
 ELEMENTS:
-- TAG: LOW_LEVEL_REQUIREMENT
+- TAG: REQUIREMENT
   FIELDS:
-  - TITLE: UID
-    TYPE: String
-    REQUIRED: True
-  - TITLE: REFS
-    TYPE: Reference(ParentReqReference, FileReference, BibReference)
-    REQUIRED: False
   - TITLE: STATEMENT
     TYPE: String
     REQUIRED: False
-
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-000
-
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-001
-
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-002
-REFS:
-- TYPE: BibRef
-  FORMAT: String
-  VALUE: SampleCiteKeyStringRef-1, "The sample BibReference String-Format"
-- TYPE: BibRef
-  FORMAT: BibTex
-  VALUE: @book{hawking1989brief, title={A Brief History of Time: From the Big Bang to Black Holes}, author={Hawking, Stephen}, isbn={9780553176988}, year={1989}, publisher={Bantam Books} }
-""".lstrip()  # noqa: E501
-
-    reader = SDReader()
-
-    document = reader.read(sdoc_input)
-    assert isinstance(document, Document)
-
-    ll_requirement = document.section_contents[2]
-    references = ll_requirement.references
-    assert len(references) == 2
-
-    reference = references[0]
-    assert isinstance(reference, BibReference)
-    assert reference.ref_type == ReferenceType.BIB_REF
-    assert (
-        reference.bib_entry.bib_value == "SampleCiteKeyStringRef-1, "
-        '"The sample BibReference String-Format"'
-    )
-
-    reference = references[1]
-    assert isinstance(reference, BibReference)
-    assert reference.ref_type == ReferenceType.BIB_REF
-    assert reference.bib_entry.bib_value == (
-        "@book{hawking1989brief, "
-        "title={A Brief History of Time: From the Big Bang to Black Holes}, "
-        "author={Hawking, Stephen}, "
-        "isbn={9780553176988}, "
-        "year={1989}, "
-        "publisher={Bantam Books} "
-        "}"
-    )  # noqa: E501
-
-    writer = SDWriter()
-    output = writer.write(document)
-
-    assert sdoc_input == output
-
-
-def test_169_grammar_refs_bib_only():
-    sdoc_input = """
-[DOCUMENT]
-TITLE: Test Doc
-
-[GRAMMAR]
-ELEMENTS:
-- TAG: LOW_LEVEL_REQUIREMENT
-  FIELDS:
-  - TITLE: UID
+  - TITLE: MY_FIELD
     TYPE: String
     REQUIRED: True
   - TITLE: REFS
-    TYPE: Reference(BibReference)
-    REQUIRED: False
-  - TITLE: STATEMENT
-    TYPE: String
+    TYPE: Reference(ParentReqReference)
     REQUIRED: False
 
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-001
-
-[LOW_LEVEL_REQUIREMENT]
-UID: ID-002
-REFS:
-- TYPE: Parent
-  VALUE: ID-001
-- TYPE: BibRef
-  FORMAT: BibTex
-  VALUE: @book{hawking1989brief, title={A Brief History of Time: From the Big Bang to Black Holes}, author={Hawking, Stephen}, isbn={9780553176988}, year={1989}, publisher={Bantam Books} }
-""".lstrip()  # noqa: E501
-
-    reader = SDReader()
-    with pytest.raises(Exception) as exc_info:
-        _ = reader.read(sdoc_input)
-
-    assert exc_info.type is StrictDocSemanticError
-
-    assert re.fullmatch(
-        "Requirement field of type Reference has an unsupported Reference "
-        'Type item: ParentReqReference\\(.*ref_uid = "ID-001".*\\).',
-        exc_info.value.args[0],
-    )
-
-
-def test_edge_case_01_minimal_requirement():
-    sdoc_input = """
-[DOCUMENT]
-TITLE: Test Doc
-
-[REQUIREMENT]
-""".lstrip()
-
-    reader = SDReader()
-
-    document: Document = reader.read(sdoc_input)
-    assert isinstance(document, Document)
-
-    requirement: Requirement = document.section_contents[0]
-    assert requirement.reserved_uid is None
-    assert requirement.reserved_title is None
-    assert requirement.reserved_statement is None
-
-    writer = SDWriter()
-    output = writer.write(document)
-
-    assert sdoc_input == output
-
-
-def test_edge_case_02_uid_present_but_empty_with_no_space_character():
-    # Note: There is no whitespace character after "UID:".
-    sdoc_input = """
-[DOCUMENT]
-TITLE: Test Doc
-
-[REQUIREMENT]
-UID:
-""".lstrip()
-
-    reader = SDReader()
-
-    with pytest.raises(Exception) as exc_info:
-        _ = reader.read(sdoc_input)
-
-    assert exc_info.type is TextXSyntaxError
-    assert "Expected ' '" == exc_info.value.args[0].decode("utf-8")
-
-
-def test_edge_case_03_uid_present_but_empty_with_space_character():
-    # Note: There is a whitespace character after "UID:".
-    sdoc_input = """
-[DOCUMENT]
-TITLE: Test Doc
-
-[REQUIREMENT]
-UID: 
-""".lstrip()  # noqa: W291
-
-    reader = SDReader()
-
-    with pytest.raises(Exception) as exc_info:
-        _ = reader.read(sdoc_input)
-
-    assert exc_info.type is TextXSyntaxError
-    assert "Expected SingleLineString or '>>>\\n'" in exc_info.value.args[
-        0
-    ].decode("utf-8")
-
-
-def test_edge_case_04_uid_present_but_empty_with_two_space_characters():
-    # Note: There are two whitespace characters after "UID:".
-    sdoc_input = """
-[DOCUMENT]
-TITLE: Test Doc
-
-[REQUIREMENT]
-UID:  
-""".lstrip()  # noqa: W291
-
-    reader = SDReader()
-
-    with pytest.raises(Exception) as exc_info:
-        _ = reader.read(sdoc_input)
-
-    assert exc_info.type is TextXSyntaxError
-    assert "Expected SingleLineString or '>>>\\n'" in exc_info.value.args[
-        0
-    ].decode("utf-8")
-
-
-def test_edge_case_10_empty_multiline_field():
-    sdoc_input = """
-[DOCUMENT]
-TITLE: Test Doc
-
-[REQUIREMENT]
-COMMENT: >>>
-<<<
-""".lstrip()
-
-    reader = SDReader()
-
-    with pytest.raises(Exception) as exc_info:
-        _ = reader.read(sdoc_input)
-
-    assert exc_info.type is TextXSyntaxError
-    assert (
-        "Expected '(?ms)(?!^<<<) *(?!^<<<)\\S((?!^<<<).)+'"
-        in exc_info.value.args[0].decode("utf-8")
-    )
-
-
-def test_edge_case_11_empty_multiline_field_with_one_newline():
-    sdoc_input = """
-[DOCUMENT]
-TITLE: Test Doc
-
 [REQUIREMENT]
-COMMENT: >>>
-
+MY_FIELD: >>>
+    Some text here...
+    Some text here...
+    Some text here...
 <<<
 """.lstrip()
 
-    reader = SDReader()
-
-    with pytest.raises(Exception) as exc_info:
-        _ = reader.read(sdoc_input)
-
-    assert exc_info.type is TextXSyntaxError
-    assert (
-        "Expected '(?ms)(?!^<<<) *(?!^<<<)\\S((?!^<<<).)+'"
-        in exc_info.value.args[0].decode("utf-8")
-    )
-
-
-def test_edge_case_20_empty_section_title():
-    sdoc_input = """
-[DOCUMENT]
-TITLE: Test Doc
-
-[SECTION]
-TITLE:
-
-[/SECTION]
-""".lstrip()
-
-    reader = SDReader()
-
-    with pytest.raises(Exception) as exc_info:
-        _ = reader.read(sdoc_input)
-
-    assert exc_info.type is TextXSyntaxError
-    assert "Expected 'UID: ' or 'LEVEL: ' or 'TITLE: '" == exc_info.value.args[
-        0
-    ].decode("utf-8")
-
-
-def test_edge_case_21_section_title_with_empty_space():
-    # Empty space after TITLE:
-    sdoc_input = """
-[DOCUMENT]
-TITLE: Test Doc
-
-[SECTION]
-TITLE: 
-
-[/SECTION]
-""".lstrip()  # noqa: W291
-
-    reader = SDReader()
-
-    with pytest.raises(Exception) as exc_info:
-        _ = reader.read(sdoc_input)
-
-    assert exc_info.type is TextXSyntaxError
-    assert "Expected SingleLineString" in exc_info.value.args[0].decode("utf-8")
-
-
-def test_edge_case_22_section_title_with_two_empty_spaces():
-    # Two empty spaces after TITLE:
-    sdoc_input = """
-[DOCUMENT]
-TITLE: Test Doc
-
-[SECTION]
-TITLE:  
-
-[/SECTION]
-""".lstrip()  # noqa: W291
-
-    reader = SDReader()
-
-    with pytest.raises(Exception) as exc_info:
-        _ = reader.read(sdoc_input)
-
-    assert exc_info.type is TextXSyntaxError
-    assert "Expected SingleLineString" in exc_info.value.args[0].decode("utf-8")
-
-
-def test_edge_case_23_leading_spaces_do_not_imply_empy_field():
-    sdoc_input = """
+    expected_sdoc = """
 [DOCUMENT]
 TITLE: Test Doc
 
@@ -1811,6 +1047,8 @@ def test_edge_case_23_leading_spaces_do_not_imply_empy_field():
   - TITLE: MY_FIELD
     TYPE: String
     REQUIRED: True
+  RELATIONS:
+  - TYPE: Parent
 
 [REQUIREMENT]
 MY_FIELD: >>>
@@ -1822,10 +1060,9 @@ def test_edge_case_23_leading_spaces_do_not_imply_empy_field():
 
     reader = SDReader()
 
-    document = reader.read(sdoc_input)
+    document = reader.read(input_sdoc)
     assert isinstance(document, Document)
 
     writer = SDWriter()
     output = writer.write(document)
-
-    assert sdoc_input == output
+    assert expected_sdoc == output
diff --git a/tests/unit/strictdoc/backend/sdoc/test_dsl_passthrough_grammar.py b/tests/unit/strictdoc/backend/sdoc/test_dsl_passthrough_grammar.py
new file mode 100644
index 000000000..5cd5a8c8a
--- /dev/null
+++ b/tests/unit/strictdoc/backend/sdoc/test_dsl_passthrough_grammar.py
@@ -0,0 +1,1162 @@
+import re
+
+import pytest
+
+from strictdoc.backend.sdoc.error_handling import StrictDocSemanticError
+from strictdoc.backend.sdoc.models.document import Document
+from strictdoc.backend.sdoc.models.reference import (
+    BibReference,
+    FileReference,
+    ParentReqReference,
+)
+from strictdoc.backend.sdoc.models.type_system import (
+    BibEntryFormat,
+    ReferenceType,
+)
+from strictdoc.backend.sdoc.reader import SDReader
+from strictdoc.backend.sdoc.writer import SDWriter
+
+
+def test_150_grammar_minimal_doc():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: True
+""".lstrip()
+
+    expected_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: True
+  RELATIONS:
+  - TYPE: Parent
+""".lstrip()
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert expected_sdoc == output
+
+
+def test_151_grammar_single_choice():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: SINGLE_CHOICE_FIELD
+    TYPE: SingleChoice(A, B, C)
+    REQUIRED: True
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+
+[LOW_LEVEL_REQUIREMENT]
+SINGLE_CHOICE_FIELD: A
+""".lstrip()
+
+    expected_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: SINGLE_CHOICE_FIELD
+    TYPE: SingleChoice(A, B, C)
+    REQUIRED: True
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
+
+[LOW_LEVEL_REQUIREMENT]
+SINGLE_CHOICE_FIELD: A
+""".lstrip()
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert expected_sdoc == output
+
+
+def test_152_grammar_multiple_choice():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: MULTIPLE_CHOICE_FIELD
+    TYPE: MultipleChoice(A, B, C)
+    REQUIRED: True
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+
+[LOW_LEVEL_REQUIREMENT]
+MULTIPLE_CHOICE_FIELD: A, C
+""".lstrip()
+
+    expected_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: MULTIPLE_CHOICE_FIELD
+    TYPE: MultipleChoice(A, B, C)
+    REQUIRED: True
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
+
+[LOW_LEVEL_REQUIREMENT]
+MULTIPLE_CHOICE_FIELD: A, C
+""".lstrip()
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert expected_sdoc == output
+
+
+def test_153_grammar_tag():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: TAG_FIELD
+    TYPE: Tag
+    REQUIRED: True
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+
+[LOW_LEVEL_REQUIREMENT]
+TAG_FIELD: A, C
+""".lstrip()
+
+    expected_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: TAG_FIELD
+    TYPE: Tag
+    REQUIRED: True
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
+
+[LOW_LEVEL_REQUIREMENT]
+TAG_FIELD: A, C
+""".lstrip()
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert expected_sdoc == output
+
+
+def test_154_grammar_multiline_custom_field():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: REQUIREMENT
+  FIELDS:
+  - TITLE: MY_FIELD
+    TYPE: String
+    REQUIRED: True
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+
+[REQUIREMENT]
+MY_FIELD: >>>
+Some text here...
+Some text here...
+Some text here...
+<<<
+""".lstrip()
+
+    expected_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: REQUIREMENT
+  FIELDS:
+  - TITLE: MY_FIELD
+    TYPE: String
+    REQUIRED: True
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
+
+[REQUIREMENT]
+MY_FIELD: >>>
+Some text here...
+Some text here...
+Some text here...
+<<<
+""".lstrip()
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert expected_sdoc == output
+
+
+def test_160_grammar_refs():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: UID
+    TYPE: String
+    REQUIRED: True
+  - TITLE: REFS
+    TYPE: Reference(ParentReqReference, FileReference, BibReference)
+    REQUIRED: False
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-000
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-001
+REFS:
+- TYPE: File
+  VALUE: /tmp/sample0.cpp
+- TYPE: Parent
+  VALUE: ID-000
+- TYPE: BibRef
+  FORMAT: BibTex
+  VALUE: @book{hawking1989brief, title={A Brief History of Time: From the Big Bang to Black Holes}, author={Hawking, Stephen}, isbn={9780553176988}, year={1989}, publisher={Bantam Books} }
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-002
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+- TYPE: File
+  VALUE: /tmp/sample1.cpp
+- TYPE: File
+  VALUE: /tmp/sample2.cpp
+- TYPE: BibRef
+  FORMAT: String
+  VALUE: SampleCiteKeyStringRef-1, "The sample BibReference String-Format"
+""".lstrip()  # noqa: E501
+
+    expected_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: UID
+    TYPE: String
+    REQUIRED: True
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
+  - TYPE: File
+  - TYPE: Bibtex
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-000
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-001
+REFS:
+- TYPE: File
+  VALUE: /tmp/sample0.cpp
+- TYPE: Parent
+  VALUE: ID-000
+- TYPE: BibRef
+  FORMAT: BibTex
+  VALUE: @book{hawking1989brief, title={A Brief History of Time: From the Big Bang to Black Holes}, author={Hawking, Stephen}, isbn={9780553176988}, year={1989}, publisher={Bantam Books} }
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-002
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+- TYPE: File
+  VALUE: /tmp/sample1.cpp
+- TYPE: File
+  VALUE: /tmp/sample2.cpp
+- TYPE: BibRef
+  FORMAT: String
+  VALUE: SampleCiteKeyStringRef-1, "The sample BibReference String-Format"
+""".lstrip()  # noqa: E501
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    ll_requirement = document.section_contents[2]
+    references = ll_requirement.references
+    assert len(references) == 4
+
+    reference = references[0]
+    assert isinstance(reference, ParentReqReference)
+    assert reference.ref_type == ReferenceType.PARENT
+    assert reference.ref_uid == "ID-001"
+
+    reference: FileReference = references[1]
+    assert reference.ref_type == ReferenceType.FILE
+    assert isinstance(reference, FileReference)
+    assert reference.g_file_entry.g_file_path == "/tmp/sample1.cpp"
+
+    reference = references[2]
+    assert reference.ref_type == ReferenceType.FILE
+    assert isinstance(reference, FileReference)
+    assert reference.g_file_entry.g_file_path == "/tmp/sample2.cpp"
+
+    reference = references[3]
+    assert reference.ref_type == ReferenceType.BIB_REF
+    assert isinstance(reference, BibReference)
+    assert (
+        reference.bib_entry.bib_value == "SampleCiteKeyStringRef-1, "
+        '"The sample BibReference String-Format"'
+    )
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert expected_sdoc == output
+
+
+def test_161_grammar_refs_file():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: REFS
+    TYPE: Reference(ParentReqReference, FileReference, BibReference)
+    REQUIRED: False
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+
+[LOW_LEVEL_REQUIREMENT]
+REFS:
+- TYPE: File
+  VALUE: /tmp/sample.cpp
+""".lstrip()
+
+    expected_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
+  - TYPE: File
+  - TYPE: Bibtex
+
+[LOW_LEVEL_REQUIREMENT]
+REFS:
+- TYPE: File
+  VALUE: /tmp/sample.cpp
+""".lstrip()
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    ll_requirement = document.section_contents[0]
+    references = ll_requirement.references
+    assert len(references) == 1
+
+    reference: FileReference = references[0]
+    assert isinstance(reference, FileReference)
+    assert reference.ref_type == ReferenceType.FILE
+    assert reference.g_file_entry.g_file_path == "/tmp/sample.cpp"
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert expected_sdoc == output
+
+
+def test_162_grammar_refs_file_multi():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: REFS
+    TYPE: Reference(ParentReqReference, FileReference, BibReference)
+    REQUIRED: False
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+
+[LOW_LEVEL_REQUIREMENT]
+REFS:
+- TYPE: File
+  VALUE: /tmp/sample1.cpp
+- TYPE: File
+  VALUE: /tmp/sample2.cpp
+- TYPE: File
+  VALUE: /tmp/sample3.cpp
+""".lstrip()
+
+    expected_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
+  - TYPE: File
+  - TYPE: Bibtex
+
+[LOW_LEVEL_REQUIREMENT]
+REFS:
+- TYPE: File
+  VALUE: /tmp/sample1.cpp
+- TYPE: File
+  VALUE: /tmp/sample2.cpp
+- TYPE: File
+  VALUE: /tmp/sample3.cpp
+""".lstrip()
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    ll_requirement = document.section_contents[0]
+    references = ll_requirement.references
+    assert len(references) == 3
+
+    reference: FileReference = references[0]
+    assert isinstance(reference, FileReference)
+    assert reference.ref_type == ReferenceType.FILE
+    assert reference.g_file_entry.g_file_path == "/tmp/sample1.cpp"
+
+    reference = references[1]
+    assert isinstance(reference, FileReference)
+    assert reference.ref_type == ReferenceType.FILE
+    assert reference.g_file_entry.g_file_path == "/tmp/sample2.cpp"
+
+    reference = references[2]
+    assert isinstance(reference, FileReference)
+    assert reference.ref_type == ReferenceType.FILE
+    assert reference.g_file_entry.g_file_path == "/tmp/sample3.cpp"
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert expected_sdoc == output
+
+
+def test_163_grammar_refs_file_only():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: UID
+    TYPE: String
+    REQUIRED: True
+  - TITLE: REFS
+    TYPE: Reference(FileReference)
+    REQUIRED: False
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-001
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-002
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+- TYPE: File
+  VALUE: /tmp/sample1.cpp
+""".lstrip()
+
+    reader = SDReader()
+    with pytest.raises(Exception) as exc_info:
+        _ = reader.read(input_sdoc)
+
+    assert exc_info.type is StrictDocSemanticError
+    assert re.fullmatch(
+        "Requirement field of type Reference has an unsupported Reference "
+        'Type item: ParentReqReference\\(.*ref_uid = "ID-001".*\\).',
+        exc_info.value.args[0],
+    )
+
+
+def test_164_grammar_refs_parent():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: UID
+    TYPE: String
+    REQUIRED: True
+  - TITLE: REFS
+    TYPE: Reference(ParentReqReference, FileReference, BibReference)
+    REQUIRED: False
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-000
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-001
+REFS:
+- TYPE: File
+  VALUE: /tmp/sample0.cpp
+- TYPE: Parent
+  VALUE: ID-000
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-002
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+""".lstrip()
+
+    expected_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: UID
+    TYPE: String
+    REQUIRED: True
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
+  - TYPE: File
+  - TYPE: Bibtex
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-000
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-001
+REFS:
+- TYPE: File
+  VALUE: /tmp/sample0.cpp
+- TYPE: Parent
+  VALUE: ID-000
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-002
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+""".lstrip()
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    ll_requirement = document.section_contents[2]
+    references = ll_requirement.references
+    assert len(references) == 1
+
+    reference = references[0]
+    assert isinstance(reference, ParentReqReference)
+    assert reference.ref_type == ReferenceType.PARENT
+    assert reference.ref_uid == "ID-001"
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert expected_sdoc == output
+
+
+def test_165_grammar_refs_parent_multi():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: UID
+    TYPE: String
+    REQUIRED: True
+  - TITLE: REFS
+    TYPE: Reference(ParentReqReference, FileReference, BibReference)
+    REQUIRED: False
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-000
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-001
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-002
+REFS:
+- TYPE: Parent
+  VALUE: ID-000
+- TYPE: Parent
+  VALUE: ID-001
+""".lstrip()
+
+    expected_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: UID
+    TYPE: String
+    REQUIRED: True
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
+  - TYPE: File
+  - TYPE: Bibtex
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-000
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-001
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-002
+REFS:
+- TYPE: Parent
+  VALUE: ID-000
+- TYPE: Parent
+  VALUE: ID-001
+""".lstrip()
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    ll_requirement = document.section_contents[2]
+    references = ll_requirement.references
+    assert len(references) == 2
+
+    reference = references[0]
+    assert isinstance(reference, ParentReqReference)
+    assert reference.ref_type == ReferenceType.PARENT
+    assert reference.ref_uid == "ID-000"
+
+    reference = references[1]
+    assert isinstance(reference, ParentReqReference)
+    assert reference.ref_type == ReferenceType.PARENT
+    assert reference.ref_uid == "ID-001"
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert expected_sdoc == output
+
+
+def test_166_grammar_refs_parent_only():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: UID
+    TYPE: String
+    REQUIRED: True
+  - TITLE: REFS
+    TYPE: Reference(ParentReqReference)
+    REQUIRED: False
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-001
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-002
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+- TYPE: File
+  VALUE: /tmp/sample1.cpp
+""".lstrip()
+
+    reader = SDReader()
+    with pytest.raises(Exception) as exc_info:
+        _ = reader.read(input_sdoc)
+
+    assert exc_info.type is StrictDocSemanticError
+
+    assert re.fullmatch(
+        "Requirement field of type Reference has an unsupported Reference"
+        " Type item: FileReference\\(.*\\).",
+        exc_info.value.args[0],
+    )
+
+
+def test_167_grammar_refs_bib():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: UID
+    TYPE: String
+    REQUIRED: True
+  - TITLE: REFS
+    TYPE: Reference(ParentReqReference, FileReference, BibReference)
+    REQUIRED: False
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-000
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-001
+REFS:
+- TYPE: File
+  VALUE: /tmp/sample0.cpp
+- TYPE: Parent
+  VALUE: ID-000
+- TYPE: BibRef
+  FORMAT: BibTex
+  VALUE: @book{hawking1989brief, title={A Brief History of Time: From the Big Bang to Black Holes}, author={Hawking, Stephen}, isbn={9780553176988}, year={1989}, publisher={Bantam Books} }
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-002
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+- TYPE: BibRef
+  FORMAT: String
+  VALUE: SampleCiteKeyStringRef-1, "The sample BibReference String-Format"
+- TYPE: BibRef
+  FORMAT: String
+  VALUE: SampleCiteKeyStringRef-2
+- TYPE: BibRef
+  FORMAT: Citation
+  VALUE: hawking1989brief, section 2.1
+""".lstrip()  # noqa: E501
+
+    expected_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: UID
+    TYPE: String
+    REQUIRED: True
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
+  - TYPE: File
+  - TYPE: Bibtex
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-000
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-001
+REFS:
+- TYPE: File
+  VALUE: /tmp/sample0.cpp
+- TYPE: Parent
+  VALUE: ID-000
+- TYPE: BibRef
+  FORMAT: BibTex
+  VALUE: @book{hawking1989brief, title={A Brief History of Time: From the Big Bang to Black Holes}, author={Hawking, Stephen}, isbn={9780553176988}, year={1989}, publisher={Bantam Books} }
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-002
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+- TYPE: BibRef
+  FORMAT: String
+  VALUE: SampleCiteKeyStringRef-1, "The sample BibReference String-Format"
+- TYPE: BibRef
+  FORMAT: String
+  VALUE: SampleCiteKeyStringRef-2
+- TYPE: BibRef
+  FORMAT: Citation
+  VALUE: hawking1989brief, section 2.1
+""".lstrip()  # noqa: E501
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    ll_requirement = document.section_contents[2]
+    references = ll_requirement.references
+    assert len(references) == 4
+
+    reference = references[1]
+    assert isinstance(reference, BibReference)
+    assert reference.ref_type == ReferenceType.BIB_REF
+    assert reference.bib_entry.bib_format == BibEntryFormat.STRING
+    assert (
+        reference.bib_entry.bib_value == "SampleCiteKeyStringRef-1,"
+        ' "The sample BibReference'
+        ' String-Format"'
+    )
+    assert reference.bib_entry.ref_cite == "SampleCiteKeyStringRef-1"
+    assert (
+        reference.bib_entry.ref_detail
+        == '"The sample BibReference String-Format"'
+    )
+    assert reference.bib_entry.bibtex_entry.type == "misc"
+    assert (
+        reference.bib_entry.bibtex_entry.fields["note"]
+        == '"The sample BibReference String-Format"'
+    )
+
+    reference = references[2]
+    assert isinstance(reference, BibReference)
+    assert reference.ref_type == ReferenceType.BIB_REF
+    assert reference.bib_entry.bib_format == BibEntryFormat.STRING
+    assert reference.bib_entry.bib_value == "SampleCiteKeyStringRef-2"
+    assert reference.bib_entry.ref_cite == "SampleCiteKeyStringRef-2"
+    assert reference.bib_entry.ref_detail is None
+    assert reference.bib_entry.bibtex_entry is None
+
+    reference = references[3]
+    assert isinstance(reference, BibReference)
+    assert reference.ref_type == ReferenceType.BIB_REF
+    assert reference.bib_entry.bib_format == BibEntryFormat.CITATION
+    assert reference.bib_entry.bib_value == "hawking1989brief, section 2.1"
+    assert reference.bib_entry.ref_cite == "hawking1989brief"
+    assert reference.bib_entry.ref_detail == "section 2.1"
+    assert reference.bib_entry.bibtex_entry is None
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert expected_sdoc == output
+
+
+def test_168_grammar_refs_bib_multi():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: UID
+    TYPE: String
+    REQUIRED: True
+  - TITLE: REFS
+    TYPE: Reference(ParentReqReference, FileReference, BibReference)
+    REQUIRED: False
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-000
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-001
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-002
+REFS:
+- TYPE: BibRef
+  FORMAT: String
+  VALUE: SampleCiteKeyStringRef-1, "The sample BibReference String-Format"
+- TYPE: BibRef
+  FORMAT: BibTex
+  VALUE: @book{hawking1989brief, title={A Brief History of Time: From the Big Bang to Black Holes}, author={Hawking, Stephen}, isbn={9780553176988}, year={1989}, publisher={Bantam Books} }
+""".lstrip()  # noqa: E501
+
+    expected_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: UID
+    TYPE: String
+    REQUIRED: True
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+  RELATIONS:
+  - TYPE: Parent
+  - TYPE: File
+  - TYPE: Bibtex
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-000
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-001
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-002
+REFS:
+- TYPE: BibRef
+  FORMAT: String
+  VALUE: SampleCiteKeyStringRef-1, "The sample BibReference String-Format"
+- TYPE: BibRef
+  FORMAT: BibTex
+  VALUE: @book{hawking1989brief, title={A Brief History of Time: From the Big Bang to Black Holes}, author={Hawking, Stephen}, isbn={9780553176988}, year={1989}, publisher={Bantam Books} }
+""".lstrip()  # noqa: E501
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    ll_requirement = document.section_contents[2]
+    references = ll_requirement.references
+    assert len(references) == 2
+
+    reference = references[0]
+    assert isinstance(reference, BibReference)
+    assert reference.ref_type == ReferenceType.BIB_REF
+    assert (
+        reference.bib_entry.bib_value == "SampleCiteKeyStringRef-1, "
+        '"The sample BibReference String-Format"'
+    )
+
+    reference = references[1]
+    assert isinstance(reference, BibReference)
+    assert reference.ref_type == ReferenceType.BIB_REF
+    assert reference.bib_entry.bib_value == (
+        "@book{hawking1989brief, "
+        "title={A Brief History of Time: From the Big Bang to Black Holes}, "
+        "author={Hawking, Stephen}, "
+        "isbn={9780553176988}, "
+        "year={1989}, "
+        "publisher={Bantam Books} "
+        "}"
+    )  # noqa: E501
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert expected_sdoc == output
+
+
+def test_169_grammar_refs_bib_only():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: UID
+    TYPE: String
+    REQUIRED: True
+  - TITLE: REFS
+    TYPE: Reference(BibReference)
+    REQUIRED: False
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: False
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-001
+
+[LOW_LEVEL_REQUIREMENT]
+UID: ID-002
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+- TYPE: BibRef
+  FORMAT: BibTex
+  VALUE: @book{hawking1989brief, title={A Brief History of Time: From the Big Bang to Black Holes}, author={Hawking, Stephen}, isbn={9780553176988}, year={1989}, publisher={Bantam Books} }
+""".lstrip()  # noqa: E501
+
+    reader = SDReader()
+    with pytest.raises(Exception) as exc_info:
+        _ = reader.read(input_sdoc)
+
+    assert exc_info.type is StrictDocSemanticError
+
+    assert re.fullmatch(
+        "Requirement field of type Reference has an unsupported Reference "
+        'Type item: ParentReqReference\\(.*ref_uid = "ID-001".*\\).',
+        exc_info.value.args[0],
+    )
+
+
+def test_170_grammar_refs():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: LOW_LEVEL_REQUIREMENT
+  FIELDS:
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: True
+  RELATIONS:
+  - TYPE: Parent
+  - TYPE: Parent
+    ROLE: Refines
+  - TYPE: Child
+    ROLE: Refined_by
+
+[LOW_LEVEL_REQUIREMENT]
+STATEMENT: This is a statement.
+""".lstrip()
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert input_sdoc == output
diff --git a/tests/unit/strictdoc/backend/sdoc/test_dsl_passthrough_refs.py b/tests/unit/strictdoc/backend/sdoc/test_dsl_passthrough_refs.py
new file mode 100644
index 000000000..d5126bfd3
--- /dev/null
+++ b/tests/unit/strictdoc/backend/sdoc/test_dsl_passthrough_refs.py
@@ -0,0 +1,226 @@
+from strictdoc.backend.sdoc.models.document import Document
+from strictdoc.backend.sdoc.reader import SDReader
+from strictdoc.backend.sdoc.writer import SDWriter
+
+
+def test_001_new_refs():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[REQUIREMENT]
+STATEMENT: >>>
+This is a statement.
+<<<
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+  ROLE: Refines
+""".lstrip()
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert input_sdoc == output
+
+
+def test_002_new_refs_moves_refs():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[REQUIREMENT]
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+  ROLE: Refines
+STATEMENT: >>>
+This is a statement.
+<<<
+""".lstrip()
+
+    expected_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[REQUIREMENT]
+STATEMENT: >>>
+This is a statement.
+<<<
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+  ROLE: Refines
+""".lstrip()
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert expected_sdoc == output
+
+
+def test_003_new_refs_moves_refs():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[REQUIREMENT]
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+  ROLE: Refines
+STATEMENT: >>>
+This is a statement.
+<<<
+COMMENT: >>>
+This is a comment.
+<<<
+""".lstrip()
+
+    expected_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[REQUIREMENT]
+STATEMENT: >>>
+This is a statement.
+<<<
+COMMENT: >>>
+This is a comment.
+<<<
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+  ROLE: Refines
+""".lstrip()
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert expected_sdoc == output
+
+
+def test_004_new_refs_moves_refs():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[REQUIREMENT]
+TITLE: This is a title.
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+  ROLE: Refines
+STATEMENT: >>>
+This is a statement.
+<<<
+COMMENT: >>>
+This is a comment.
+<<<
+""".lstrip()
+
+    expected_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[REQUIREMENT]
+TITLE: This is a title.
+STATEMENT: >>>
+This is a statement.
+<<<
+COMMENT: >>>
+This is a comment.
+<<<
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+  ROLE: Refines
+""".lstrip()
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert expected_sdoc == output
+
+
+def test_005_new_refs_with_correct_grammar():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[GRAMMAR]
+ELEMENTS:
+- TAG: REQUIREMENT
+  FIELDS:
+  - TITLE: STATEMENT
+    TYPE: String
+    REQUIRED: True
+  RELATIONS:
+  - TYPE: Parent
+    ROLE: Refines
+
+[REQUIREMENT]
+STATEMENT: >>>
+This is a statement.
+<<<
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+  ROLE: Refines
+""".lstrip()
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert input_sdoc == output
+
+
+def test_020_parent_ref_with_relation():
+    input_sdoc = """
+[DOCUMENT]
+TITLE: Test Doc
+
+[REQUIREMENT]
+STATEMENT: >>>
+This is a statement.
+<<<
+REFS:
+- TYPE: Parent
+  VALUE: ID-001
+  ROLE: Refines
+""".lstrip()
+
+    reader = SDReader()
+
+    document = reader.read(input_sdoc)
+    assert isinstance(document, Document)
+
+    writer = SDWriter()
+    output = writer.write(document)
+
+    assert input_sdoc == output