diff --git a/.gitignore b/.gitignore
index 3f3383f92..4cfca3148 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,8 +3,9 @@
 *.pyc
 local_settings.py
 *.egg-info
-.treerc
 .coverage
+.tox
+.treerc
 htmlcov
 *~
 
diff --git a/MANIFEST.in b/MANIFEST.in
index e69de29bb..3c1402c64 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -0,0 +1 @@
+include xblock/VERSION.txt
diff --git a/requirements.txt b/requirements.txt
index 0e3da7285..2dc9c9abf 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -3,6 +3,7 @@ pyyaml
 lxml
 webob>=1.6.0
 simplejson
+six
 pytz
 python-dateutil
 markupsafe
diff --git a/script/max_pylint_violations b/script/max_pylint_violations
index 099261d78..d935e532d 100755
--- a/script/max_pylint_violations
+++ b/script/max_pylint_violations
@@ -1,10 +1,10 @@
 #!/bin/bash
-DEFAULT_MAX=11
+DEFAULT_MAX=8
 
 pylint xblock | tee /tmp/pylint-xblock.log
 ERR=`grep -E "^[C|R|W|E]:" /tmp/pylint-xblock.log | wc -l`
 MAX=${1-$DEFAULT_MAX}
-if [ $ERR -ge $MAX ]; then
+if [ $ERR -gt $MAX ]; then
     echo "too many pylint violations: $ERR (max is $MAX)"
     exit 1
 else
diff --git a/setup.py b/setup.py
old mode 100644
new mode 100755
index 0e78473c3..1101c3361
--- a/setup.py
+++ b/setup.py
@@ -1,9 +1,17 @@
-"""Set up for XBlock"""
+#!/usr/bin/env python
+
+"""
+Set up for XBlock
+"""
+
+import os.path
 from setuptools import setup
 
+version_file = os.path.join(os.path.dirname(__file__), 'xblock/VERSION.txt')
+
 setup(
     name='XBlock',
-    version='0.4.12',
+    version=open(version_file).read().strip(),
     description='XBlock Core Library',
     packages=[
         'xblock',
@@ -12,14 +20,16 @@
         'xblock.test',
         'xblock.test.django',
     ],
+    include_package_data=True,
     install_requires=[
+        'fs',
         'lxml',
         'markupsafe',
         'python-dateutil',
         'pytz',
         'pyyaml',
+        'six',
         'webob',
-        'fs',
     ],
     extras_require={
         'django': ['django-pyfs']
diff --git a/xblock/VERSION.txt b/xblock/VERSION.txt
new file mode 100644
index 000000000..1f7716999
--- /dev/null
+++ b/xblock/VERSION.txt
@@ -0,0 +1 @@
+0.4.13
diff --git a/xblock/__init__.py b/xblock/__init__.py
index 49bc3d3c9..27a1cc562 100644
--- a/xblock/__init__.py
+++ b/xblock/__init__.py
@@ -2,8 +2,7 @@
 XBlock Courseware Components
 """
 
-# For backwards compatability, provide the XBlockMixin in xblock.fields
-# without causing a circular import
+import os
 import warnings
 import xblock.core
 import xblock.fields
@@ -20,6 +19,10 @@ def __init__(self, *args, **kwargs):
         super(XBlockMixin, self).__init__(*args, **kwargs)
 
 
+# For backwards compatability, provide the XBlockMixin in xblock.fields
+# without causing a circular import
 xblock.fields.XBlockMixin = XBlockMixin
 
-__version__ = "0.4.7"
+VERSION_FILE = os.path.join(os.path.dirname(__file__), 'VERSION.txt')
+
+__version__ = open(VERSION_FILE).read().strip()
diff --git a/xblock/fields.py b/xblock/fields.py
index a210c7730..d270ee340 100644
--- a/xblock/fields.py
+++ b/xblock/fields.py
@@ -9,24 +9,26 @@
 from collections import namedtuple
 import copy
 import datetime
-import dateutil.parser
 import hashlib
 import itertools
-import pytz
+import json
 import traceback
+import unicodedata
 import warnings
-import json
+
+import dateutil.parser
+from lxml import etree
+import pytz
+import six
 import yaml
-import unicodedata
 
 from xblock.internal import Nameable
 
-
 # __all__ controls what classes end up in the docs, and in what order.
 __all__ = [
     'BlockScope', 'UserScope', 'Scope', 'ScopeIds',
     'Field',
-    'Boolean', 'Dict', 'Float', 'Integer', 'List', 'Set', 'String',
+    'Boolean', 'Dict', 'Float', 'Integer', 'List', 'Set', 'String', 'XMLString',
     'XBlockMixin',
 ]
 
@@ -832,6 +834,19 @@ class String(JSONField):
 
     """
     MUTABLE = False
+    VALID_CONTROLS = {u'\n', u'\r', u'\t'}
+
+    def _valid_unichar(self, character):
+        """
+        Strip invalid control characters from a unicode text object.
+        """
+        return unicodedata.category(character)[0] != u'C' or character in self.VALID_CONTROLS
+
+    def _valid_bytechar(self, character):
+        """
+        Strip invalid control characters from a bytestring object.
+        """
+        return ord(character) >= 32 or character.decode('ascii', errors='replace') in self.VALID_CONTROLS
 
     def _sanitize(self, value):
         """
@@ -839,10 +854,10 @@ def _sanitize(self, value):
         https://www.w3.org/TR/xml/#charsets
         Leave all other characters.
         """
-        if isinstance(value, unicode):
-            new_value = u''.join(ch for ch in value if unicodedata.category(ch)[0] != u'C' or ch in (u'\n', u'\r', u'\t'))
-        elif isinstance(value, str):
-            new_value = ''.join(ch for ch in value if ord(ch) >= 32 or ch in ('\n', '\r', '\t'))
+        if isinstance(value, six.text_type):
+            new_value = u''.join(ch for ch in value if self._valid_unichar(ch))
+        elif isinstance(value, six.binary_type):
+            new_value = b''.join(ch for ch in value if self._valid_bytechar(ch))
         else:
             return value
         # The new string will be equivalent to the original string if no control characters are present.
@@ -871,6 +886,32 @@ def none_to_xml(self):
     enforce_type = from_json
 
 
+class XMLString(String):
+    """
+    A field class for representing an XML string.
+
+    The value, as loaded or enforced, can either be None or a basestring instance.
+    If it is a basestring instance, it must be valid XML.  If it is not valid XML,
+    an lxml.etree.XMLSyntaxError will be raised.
+    """
+
+    def to_json(self, value):
+        """
+        Serialize the data, ensuring that it is valid XML (or None).
+
+        Raises an lxml.etree.XMLSyntaxError if it is a basestring but not valid
+        XML.
+        """
+        if self._enable_enforce_type:
+            value = self.enforce_type(value)
+        return super(XMLString, self).to_json(value)
+
+    def enforce_type(self, value):
+        if value is not None:
+            etree.XML(value)
+        return value
+
+
 class DateTime(JSONField):
     """
     A field for representing a datetime.
diff --git a/xblock/test/test_fields.py b/xblock/test/test_fields.py
index 25325a6d4..c10425d06 100644
--- a/xblock/test/test_fields.py
+++ b/xblock/test/test_fields.py
@@ -2,34 +2,31 @@
 Tests for classes extending Field.
 """
 
-# Allow accessing protected members for testing purposes
-# pylint: disable=W0212
-
-from mock import Mock
-import unittest
+# pylint: disable=abstract-class-instantiated, protected-access
 
+from contextlib import contextmanager
 import datetime as dt
-import pytz
-import warnings
+import itertools
 import math
 import textwrap
-import itertools
-from contextlib import contextmanager
+import unittest
+import warnings
 
 import ddt
+from lxml import etree
+from mock import Mock
+import pytz
 
 from xblock.core import XBlock, Scope
 from xblock.field_data import DictFieldData
 from xblock.fields import (
-    Any, Boolean, Dict, Field, Float,
-    Integer, List, Set, String, DateTime, Reference, ReferenceList, Sentinel,
-    UNIQUE_ID
+    Any, Boolean, Dict, Field, Float, Integer, List, Set, String, XMLString, DateTime, Reference, ReferenceList,
+    ScopeIds, Sentinel, UNIQUE_ID, scope_key,
 )
 
 from xblock.test.tools import (
     assert_equals, assert_not_equals, assert_in, assert_not_in, assert_false, TestRuntime
 )
-from xblock.fields import scope_key, ScopeIds
 
 
 class FieldTest(unittest.TestCase):
@@ -244,6 +241,44 @@ def test_control_characters_filtered(self):
         self.assertJSONOrSetGetEquals(u'\n\r\t', u'\n\v\r\b\t')
 
 
+@ddt.ddt
+class XMLStringTest(FieldTest):
+    """
+    Tests the XMLString Field.
+    """
+    FIELD_TO_TEST = XMLString
+
+    @ddt.data(
+        u'<abc>Hello</abc>',
+        u'<abc attr="yes">Hello</abc>',
+        u'<xml/>',
+        '<bytes/>',
+        '<unicode>\xc8\x88</unicode>',
+        None
+    )
+    def test_json_equals(self, input_text):
+        xml_string = self.FIELD_TO_TEST(enforce_type=True)
+        self.assertEqual(xml_string.to_json(input_text), input_text)
+
+    @ddt.data(
+        'text',
+        '<xml',
+        '<xml attr=3/>',
+        '<xml attr="3/>',
+        '<open>',
+        '<open>with text',
+        '<xml/>trailing text',
+        '<open>text</close>',
+        '<invalid_utf8 char="\x9e"/>',
+    )
+    def test_bad_xml(self, input_text):
+        # pylint: disable=no-member
+        xml_string = self.FIELD_TO_TEST(enforce_type=True)
+        self.assertRaises(etree.XMLSyntaxError, xml_string.to_json, input_text)
+        unchecked_xml_string = self.FIELD_TO_TEST(enforce_type=False)
+        self.assertEqual(unchecked_xml_string.to_json(input_text), input_text)
+
+
 @ddt.ddt
 class DateTest(FieldTest):
     """