diff --git a/.travis.yml b/.travis.yml
index 9acfc0e0..76a3f553 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -25,6 +25,8 @@ install:
   - git lfs pull
   - pip install -e .[full]
   - pip install -r doc/requirements.txt
+  # for pygmsh >= 7.0
+  # - sudo apt install libglu1
 
 script:
   - set -e
diff --git a/doc/requirements.txt b/doc/requirements.txt
index 918c12b3..11883eed 100644
--- a/doc/requirements.txt
+++ b/doc/requirements.txt
@@ -1,4 +1,4 @@
-pygmsh
+pygmsh==6.1.1
 seaborn
 sphinx
 sphinx-argparse
diff --git a/doc/source/api/io.rst b/doc/source/api/io.rst
index 2b4bc320..891ed1ed 100644
--- a/doc/source/api/io.rst
+++ b/doc/source/api/io.rst
@@ -8,6 +8,8 @@ Input parameters
 
 .. autofunction:: toughio.write_input
 
+.. autofunction:: toughio.register_input
+
 
 Simulation outputs
 ------------------
@@ -17,3 +19,5 @@ Simulation outputs
 .. autofunction:: toughio.read_output
 
 .. autofunction:: toughio.write_output
+
+.. autofunction:: toughio.register_output
diff --git a/doc/source/api/mesh.rst b/doc/source/api/mesh.rst
index 0a7ef762..c5cc00be 100644
--- a/doc/source/api/mesh.rst
+++ b/doc/source/api/mesh.rst
@@ -12,6 +12,8 @@ I/O
 
 .. autofunction:: toughio.write_mesh
 
+.. autofunction:: toughio.register_mesh
+
 .. autofunction:: toughio.read_time_series
 
 .. autofunction:: toughio.write_time_series
diff --git a/examples/co2_leakage_along_a_fault/1_generate_mesh_in_python_with_gmsh.py b/examples/co2_leakage_along_a_fault/1_generate_mesh_in_python_with_gmsh.py
index 2b432634..270fb42f 100644
--- a/examples/co2_leakage_along_a_fault/1_generate_mesh_in_python_with_gmsh.py
+++ b/examples/co2_leakage_along_a_fault/1_generate_mesh_in_python_with_gmsh.py
@@ -6,7 +6,7 @@
 
 .. code-block:: bash
 
-    pip install pygmsh --user
+    pip install pygmsh==6.1.1 --user
 
 The mesh can also be generated from scratch directly in Gmsh either using its GUI and/or its internal scripting language.
 
diff --git a/toughio/__about__.py b/toughio/__about__.py
index 1eb94176..bd2771d9 100644
--- a/toughio/__about__.py
+++ b/toughio/__about__.py
@@ -1,4 +1,4 @@
-__version__ = "1.4.2"
+__version__ = "1.4.3"
 __author__ = "Keurfon Luu"
 __author_email__ = "keurfonluu@lbl.gov"
 __website__ = "https://github.com/keurfonluu/toughio"
diff --git a/toughio/__init__.py b/toughio/__init__.py
index 3f14c4f6..ca5ae67b 100644
--- a/toughio/__init__.py
+++ b/toughio/__init__.py
@@ -11,12 +11,15 @@
     read_history,
     read_input,
     read_output,
+    register_input,
+    register_output,
     write_input,
     write_output,
 )
 from ._mesh import CellBlock, Mesh, from_meshio, from_pyvista
 from ._mesh import read as read_mesh
 from ._mesh import read_time_series
+from ._mesh import register as register_mesh
 from ._mesh import write as write_mesh
 from ._mesh import write_time_series
 
@@ -25,6 +28,9 @@
     "CellBlock",
     "Output",
     "meshmaker",
+    "register_input",
+    "register_output",
+    "register_mesh",
     "read_history",
     "read_input",
     "read_output",
diff --git a/toughio/_io/__init__.py b/toughio/_io/__init__.py
index 556f1eee..aa97fe2c 100644
--- a/toughio/_io/__init__.py
+++ b/toughio/_io/__init__.py
@@ -1,12 +1,16 @@
 from .input import read as read_input
+from .input import register as register_input
 from .input import write as write_input
 from .output import Output
 from .output import read as read_output
 from .output import read_history
+from .output import register as register_output
 from .output import write as write_output
 
 __all__ = [
     "Output",
+    "register_input",
+    "register_output",
     "read_input",
     "write_input",
     "read_output",
diff --git a/toughio/_io/input/__init__.py b/toughio/_io/input/__init__.py
index f2ec4105..e4b9e1a7 100644
--- a/toughio/_io/input/__init__.py
+++ b/toughio/_io/input/__init__.py
@@ -1,7 +1,8 @@
 from . import json, tough
-from ._helpers import read, write
+from ._helpers import read, register, write
 
 __all__ = [
+    "register",
     "read",
     "write",
 ]
diff --git a/toughio/_io/input/_helpers.py b/toughio/_io/input/_helpers.py
index d98047ad..2c7b2219 100644
--- a/toughio/_io/input/_helpers.py
+++ b/toughio/_io/input/_helpers.py
@@ -1,6 +1,7 @@
 from ..._common import filetype_from_filename, register_format
 
 __all__ = [
+    "register",
     "read",
     "write",
 ]
@@ -12,7 +13,21 @@
 
 
 def register(file_format, extensions, reader, writer=None):
-    """Register a new format."""
+    """
+    Register a new input format.
+
+    Parameters
+    ----------
+    file_format : str
+        File format to register.
+    extensions : array_like
+        List of extensions to associate to the new format.
+    reader : callable
+        Read fumction.
+    writer : callable or None, optional, default None
+        Write function.
+
+    """
     register_format(
         fmt=file_format,
         ext_to_fmt=_extension_to_filetype,
diff --git a/toughio/_io/output/__init__.py b/toughio/_io/output/__init__.py
index e84cd33f..9dd04a09 100644
--- a/toughio/_io/output/__init__.py
+++ b/toughio/_io/output/__init__.py
@@ -1,9 +1,10 @@
 from . import csv, petrasim, save, tecplot, tough
 from ._common import Output
-from ._helpers import read, read_history, write
+from ._helpers import read, read_history, register, write
 
 __all__ = [
     "Output",
+    "register",
     "read",
     "write",
     "read_history",
diff --git a/toughio/_io/output/_helpers.py b/toughio/_io/output/_helpers.py
index d247a1d8..cb6c0dd2 100644
--- a/toughio/_io/output/_helpers.py
+++ b/toughio/_io/output/_helpers.py
@@ -6,6 +6,7 @@
 from ._common import Output
 
 __all__ = [
+    "register",
     "read",
     "write",
     "read_history",
@@ -18,7 +19,21 @@
 
 
 def register(file_format, extensions, reader, writer=None):
-    """Register a new format."""
+    """
+    Register a new output format.
+
+    Parameters
+    ----------
+    file_format : str
+        File format to register.
+    extensions : array_like
+        List of extensions to associate to the new format.
+    reader : callable
+        Read fumction.
+    writer : callable or None, optional, default None
+        Write function.
+
+    """
     register_format(
         fmt=file_format,
         ext_to_fmt=_extension_to_filetype,
diff --git a/toughio/_mesh/__init__.py b/toughio/_mesh/__init__.py
index c5af21c0..2ca37257 100644
--- a/toughio/_mesh/__init__.py
+++ b/toughio/_mesh/__init__.py
@@ -1,10 +1,11 @@
 import meshio
 
 from . import avsucd, flac3d, pickle, tecplot, tough
-from ._helpers import read, read_time_series, write, write_time_series
+from ._helpers import read, read_time_series, register, write, write_time_series
 from ._mesh import CellBlock, Mesh, from_meshio, from_pyvista
 
 __all__ = [
+    "register",
     "read",
     "write",
     "read_time_series",
diff --git a/toughio/_mesh/_helpers.py b/toughio/_mesh/_helpers.py
index 92660cdd..08e3f478 100644
--- a/toughio/_mesh/_helpers.py
+++ b/toughio/_mesh/_helpers.py
@@ -7,6 +7,7 @@
 from ._mesh import from_meshio
 
 __all__ = [
+    "register",
     "read",
     "write",
     "read_time_series",
@@ -21,7 +22,23 @@
 
 
 def register(file_format, extensions, reader, writer=None, material=None):
-    """Register a new format."""
+    """
+    Register a new mesh format.
+
+    Parameters
+    ----------
+    file_format : str
+        File format to register.
+    extensions : array_like
+        List of extensions to associate to the new format.
+    reader : callable
+        Read fumction.
+    writer : callable or None, optional, default None
+        Write function.
+    material : str or None, optional, default None
+        Cell data key associated to material.
+
+    """
     register_format(
         fmt=file_format,
         ext_to_fmt=_extension_to_filetype,