Document real compatibility tag interpretation

Beginne mit dem Abschnitt zu Kompatibilitätstags in der Dokumentation zu den Plattform-Kompatibilitätstags und vergleiche dessen PEP-425-Reihenfolge mit den Beispielen für pip 24.3.1 im Issue. Untersuche die tatsächliche Reihenfolge, einschließlich Compressed Tag Sets und älterer cp/py-manylinux-Übereinstimmungen, und dokumentiere sie anschließend so, dass der beschriebene Algorithmus dem Verhalten von pip entspricht und die Beispiele erklärt.

Issue Description

The compatibility tag section of the documentation is lifted directly from PEP-425 and covers how compatibility tags are constructed.

However, it is incomplete and inaccurate regarding how those tags are matched by pip. The described algorithm is:

This example list is for an installer running under CPython 3.3 on a linux_x86_64 system. It is in order from most-preferred (a distribution with a compiled extension module, built for the current version of Python) to least-preferred (a pure-Python distribution built with an older version of Python):

1. cp33-cp33m-linux_x86_64
2. cp33-abi3-linux_x86_64
3. cp3-abi3-linux_x86_64
4. cp33-none-linux_x86_64*
5. cp3-none-linux_x86_64*
6. py33-none-linux_x86_64*
7. py3-none-linux_x86_64*
8. cp33-none-any
9. cp3-none-any
10. py33-none-any
11. py3-none-any
12. py32-none-any
13. py31-none-any
14. py30-none-any

This is modified by "Compressed Tag Sets" but that's not relevant to this issue.

From this we can surmise, for a CPython version X.Y:

• It can match if python is cpXY and abi is cpXY*.
• It can match if python is in cpXY, cpX and abi is abi3
• It can match if python is in cpXY, cpX, pyXY, pyX and abi is none
• It can also match any pyXZ-none-any for Z < Y

This is not the actual algorithm used by pip.

In particular I'm aware of these rules obeyed by pip in practice (but I haven't found a spec):

• It can also match any cpXZ-abi3 for Z < Y
• It can also match any pyXZ-none-manylinux* for Z < Y

Given these are valid, they must be in the ordering somewhere, and it should be documented where.

Some examples illustrating these rules (pip 24.3.1, python 3.13):

$ .venv/bin/pip --version
pip 24.3.1 from /home/mauve/dev/demo/.venv/lib/python3.13/site-packages/pip (python 3.13)

$ .venv/bin/pip install --dry-run solace_pubsubplus --no-deps --no-cache
Looking in indexes: https://artifactory/pypi/simple/
Collecting solace_pubsubplus
  Downloading https://artifactory/pypi/packages/packages/5e/33/e5923f962b89b5a63eac2c0f7493abb53e7a1054a1da580c0037fd51713f/solace_pubsubplus-1.9.0-py36-none-manylinux_2_12_x86_64.whl (4.4 MB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 4.4/4.4 MB 549.6 MB/s eta 0:00:00
Would install solace-pubsubplus-1.9.0

$ .venv/bin/pip install --dry-run argon2_cffi_bindings --no-deps --no-cache
Looking in indexes: https://artifactory/pypi/simple/
Collecting argon2_cffi_bindings
  Downloading https://artifactory/pypi/packages/packages/ec/f7/378254e6dd7ae6f31fe40c8649eea7d4832a42243acaf0f1fff9083b2bed/argon2_cffi_bindings-21.2.0-cp36-abi3-manylinux_2_17_x86_64.manylinux2014_x86_64.whl (86 kB)
Would install argon2-cffi-bindings-21.2.0

Given also that Compressed Tag Sets modify the whole algorithm, making it about set intersection, it would also be better to incorporate them into a description of the algorithm too.

Code of Conduct

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