Platform tags: Adjust to centralize history

Move history to a dedicated section (consistent with other specs). In
the main text, do not reference PEPs but just describe the current spec.
Also sketch out a few missing details.

Author: jeanas

source/specifications/platform-compatibility-tags.rst

@@ -9,13 +9,6 @@ Platform compatibility tags allow build tools to mark distributions as being
 compatible with specific platforms, and allows installers to understand which
 distributions are compatible with the system they are running on.
 
-The following PEPs contributed to this spec:
-
-1. :pep:`425`
-2. :pep:`513`
-3. :pep:`571`
-4. :pep:`599`
-5. :pep:`600`
 
 Overview
 ========
@@ -92,10 +85,14 @@ decide how to best use the ABI tag.
 Platform Tag
 ------------
 
-The platform tag is simply ``sysconfig.get_platform()`` with all
-hyphens ``-`` and periods ``.`` replaced with underscore ``_``.
+-------------------
+Basic platform tags
+-------------------
+
+In its simplest form, the platform tag is ``sysconfig.get_platform()`` with
+all hyphens ``-`` and periods ``.`` replaced with underscore ``_``.
 Until the removal of :ref:`distutils` in Python 3.12, this
-was ``distutils.util.get_platform()``.
+was ``distutils.util.get_platform()``. For example:
 
 * win32
 * linux_i386
@@ -107,32 +104,30 @@ was ``distutils.util.get_platform()``.
 -------------
 .. _manylinux:
 
-The scheme defined in :pep:`425` was insufficient for public distribution of
-wheel files (and \*nix wheel files in general) to Linux platforms, due to the
-large ecosystem of Linux platforms and subtle differences between them.
+The simple scheme above is insufficient for public distribution of wheel files
+to Linux platforms, due to the large ecosystem of Linux platforms and subtle
+differences between them.
 
-Instead, :pep:`600` defines the ``manylinux`` standard, which represents a
-common subset of Linux platforms, and allows building wheels tagged with the
+Instead, for those platforms, the ``manylinux`` standard represents a common
+subset of Linux platforms, and allows building wheels tagged with the
 ``manylinux`` platform tag which can be used across most common Linux
 distributions.
 
-There were multiple iterations of the ``manylinux`` specification, each
-representing the common subset of Linux platforms at a given point in time:
+The current standard is the future-proof ``manylinux_x_y`` standard. It defines
+tags of the form ``manylinux_x_y_arch``, where ``x`` and ``y`` are glibc major
+and minor versions supported (e.g. ``manylinux_2_24_xxx`` should work on any
+distro using glibc 2.24+), and ``arch`` is the architecture, matching the value
+of ``sysconfig.get_platform()`` on the system as in the "simple" form above.
 
-* ``manylinux1`` (:pep:`513`) supports ``x86_64`` and ``i686``
-  architectures, and is based on a compatible Linux platform from 2007.
-* ``manylinux2010`` (:pep:`571`) supports ``x86_64`` and ``i686``
-  architectures. and updates the previous specification to be based on a
-  compatible Linux platform from 2010 instead.
-* ``manylinux2014`` (:pep:`599`) adds support for a number of
-  additional architectures (``aarch64``, ``armv7l``, ``ppc64``, ``ppc64le``,
-  and ``s390x``) and updates the base platform to a compatible Linux platform
-  from 2014.
+The following older tags are still supported for backward compatibility:
 
-``manylinux_x_y`` (:pep:`600`) supersedes all previous PEPs to define a
-future-proof standard. It defines ``x`` and ``y`` as glibc major an minor
-versions supported (e.g. ``manylinux_2_24`` should work on any distro using
-glibc 2.24+). Previous tags are still supported for backward compatibility.
+* ``manylinux1`` is based on a compatible Linux platform from 2007,
+  and supports ``x86_64`` and ``i686`` architectures.
+* ``manylinux2010`` is based on a platform from 2010 and supports ``x86_64``
+  and ``i686``.
+* ``manylinux2014`` is based on a platform from 2014 and supports
+  ``x86_64``, ``i686``, ``aarch64``, ``armv7l``, ``ppc64``, ``ppc64le``,
+  and ``s390x``.
 
 In general, distributions built for older versions of the specification are
 forwards-compatible (meaning that ``manylinux1`` distributions should continue
@@ -302,3 +297,15 @@ Why is the ABI tag (the second tag) sometimes "none" in the reference implementa
     implementation at the time of writing guesses "none".  Ideally it
     would detect "py27(d|m|u)" analogous to newer versions of Python,
     but in the meantime "none" is a good enough way to say "don't know".
+
+
+History
+=======
+
+The following PEPs contributed to this spec:
+
+- :pep:`425`: initial definition of platform tags
+- :pep:`513`: defined ``manylinux1``
+- :pep:`571`: defined ``manylinux2010``
+- :pep:`599`: defined ``manylinux2014``
+- :pep:`600`: defined the ``manylinux_x_y`` scheme