diff --git a/libcxx/docs/Contributing.rst b/libcxx/docs/Contributing.rst
--- a/libcxx/docs/Contributing.rst
+++ b/libcxx/docs/Contributing.rst
@@ -33,12 +33,42 @@
 2. Update the ``include/__libcpp_version`` file
 3. Update the version number in ``docs/conf.py``
 
-Modifying feature test macros
+Modifying feature-test macros
 =============================
 
-When adding or updating feature test macros, you should update the corresponding tests.
+When adding or updating feature-test macros, you should update the corresponding tests.
 To do that, modify ``feature_test_macros`` table in the script ``utils/generate_feature_test_macro_components.py``, run it, and commit updated files.
 
+================  ==============================================================
+Field             Description
+================  ==============================================================
+name              The name of the feature-test macro.
+values            A list of tuples. One tuple contains a C++ version and the
+                  value of the feature-test marco for that C++ version.
+headers           An array with the headers that should provide the
+                  feature-test macro.
+depends           An optional string field. When this field is provided
+                  ``internal_depends`` must also be provided. The field
+                  contains the dependencies for the feature. It should contain
+                  the dependency on:
+
+                  * a compiler version,
+                  * a compiler feature-test macro,
+                  * a CMake generated define, or
+                  * a macro defined in ``include/__availability``.
+
+                  It shall not depend on a macro defined in ``include/__config``.
+internal_depends  An optional string field. When this field is provided
+                  ``depends`` must also be provided. It contains the dependency:
+
+                  * when available, a macro defined in ``include/__config``,
+                  * otherwise the same as ``depends``.
+unimplemented     An optional Boolean field with the value ``True``. This field
+                  is only used when a feature isn't fully implemented. Once
+                  fully implemented the field shall be removed.
+================  ==============================================================
+
+
 Adding a new header TODO
 ========================
 
@@ -55,3 +85,12 @@
 When exporting new symbols from libc++, one must update the ABI lists located in ``lib/abi``.
 To test whether the lists are up-to-date, please run the target ``check-cxx-abilist``.
 To regenerate the lists, use the target ``generate-cxx-abilist``.
+The ABI lists must be updated all supported platforms; currently Linux and Apple.
+If you don't have access to one of these platforms an updated list can be
+downloaded from the failed build at
+`Buildkite <https://buildkite.com/llvm-project/libcxx-ci>`__.
+Look for the failed build and select the ``artifacts`` tab. There download the
+abilist for the plafform, e.g.:
+
+* C++20 for the Linux platform.
+* MacOS C++20 for the Apple platform.