As discussed on pypa/packaging.python.org#955 , this (finally!) migrates the content of PEP 517, PEP 518 and PEP 660 to the specifications section and glossary, and updates the various references throughout the site, specs and glossary to the PEPs, their contents and the terms they define to refer to, and accurately reflect, the newly canonical content spec and glossary content.
Overall, while I did put a lot of effort into diligently taking advantage of the appropriate reST syntax/directives/roles and Sphinx cross referencing for consistent source formatting and output rendering, implementing editorial corrections for organization, clarity and consistency, and making some limited and motivated additions and updates to the non-normative portions (mostly added introductory/connecting material and updating/fleshing out examples), I attempted to be conservative and avoid any substantive changes to the actual content of the normative specification, which can be discussed and applied subsequent to this initial PR.
I’d appreciate anyone interest to review the PR, to both check for editorial correctness and ensure it accurately reflects the PEPs on which it is based. Please see the issue and PR threads for more detail on the final high-level organization and motivations behind it, and other considerations to keep in mind when reviewing. Thanks, and hope to get this finally merged soon!