Language Feature Integration Document: JEPS

[rnveach]

Identified at #14904 (comment) ,

Probably JEPS should be first so the user understands what the new feature is before diving into examining existing checks.

Then looking at Review Associated JEP's Recommendations, it seems like we are splitting apart the same information.

Going with above, I think we should have a common review the JEPs and understand the change better, then updating and creating new checks can talk about their individual specifics that the global started their thinking process.

[nrmancuso]

We can come back to this after some tracker issues have been completed and we have some more experience.

[mahfouz72]

We should also extend our check update docs to always consider this check when new keywords are added to the language.

leaving this for just a remainder

Edit from @nrmancuso: the check we are referring to is IllegallIdentifier

#15105