I opened a PR with some clarifications, copyedits and other fixes:
Also, for those interested, @pf_moore 's aforementioned thread above is here:
I had a few additional, more substantive questions and comments on the PEP text:
Tools generating metadata MUST raise an error if an invalid extra name is provided as appropriate for the specified core metadata version. If an older core metadata version is specified and the name would be invalid with newer core metadata versions, tools SHOULD warn the user.
How is the core metadata version determined/specified? AFAIK, there is no user-facing way to specify this, at least in the build backends I’m familiar with. Per the discussion in @pf_moore 's thread, should this just be the latest and we can just simplify this to just raise an error if an invalid extra names is provided (since the core metadata spec is only specifying the current version, I’m not sure it makes sense to discuss older versions)?
Tools SHOULD warn users when an invalid extra name is read and SHOULD not use the name to avoid ambiguity.
What does it mean to “not use the name”? Should tools error out? Or just not write/install the extra? That seems like rather unexpected and undesirable behavior; if the tool is going to not just try to use the name anyway (presumably with normalization), it would be better to just error out rather than do something other than what the user explicitly requested.
Moving to PEP 503 normalization and PEP 508 name acceptance, it allows for all preexisting, valid names to continue to be valid.
Perhaps this should be clarified to say that valid extras specifiers per PEP 508 will continue to remain valid, since as mentioned above, this isn’t strictly true for the existing spec for Provides-Extra in core metadata.