Merge pull request #2421 from larsoner/abi3

DOC: Document abi3 status

Author: isuruf

docs/maintainer/knowledge_base.md

@@ -1466,6 +1466,15 @@ Currently available packages:
 - exceptiongroup
 - importlib-metadata
 
+<a id="abi3"></a>
+
+### Packages with abi3 extensions
+
+Packages can be built using CPython's stable [`abi3` mode](https://docs.python.org/3/c-api/stable.html) by adding a few conditionals to the `build`, `requirements`, and (optionally) `test` sections. See [this `meta.yaml` example](https://github.com/conda-forge/python-abi3-feedstock/blob/main/recipe/example-meta.yaml) from the `python-abi3-feedstock`, in particular the parts that depend on the `is_abi3`, as well as the relevant [conda-build documentation](https://docs.conda.io/projects/conda-build/en/stable/resources/define-metadata.html#python-version-independent-packages).
+
+Note that the python extension that is being packaged needs to support building the extension as an ABI3 package. For setuptools
+based projects, the keyword argument `py_limited_api=True` needs to be passed to the `setup` function.
+
 <a id="noarch-builds"></a>
 
 ## Noarch builds