Specify that tag names are case-sensitive

[rvedotrc]

It's not currently stated whether tags are case-sensitive or -insensitive (principally, for matching a tag on an Operation to a Tag object). This PR seeks to rectify that.

Or, maybe we should define them as case insensitive.

[ralfhandl]

Checked with a popular OAD display tool, and it treats tags case-sensitive.

[ralfhandl]

@tsc: how are typical tools dealing with tags that differ only in case?

[handrews]

@ralfhandl We already require them to be case-sensitive. This is a bit more clear in 3.1.1 and 3.0.4 where there is now an "HTTP and Case-Sensitivity" section noting that everything is case-sensitive unless it directly maps to an HTTP concept that is defined as case-insensitive. Tags clearly are not in the HTTP category, so they are case-sensitive.

[ralfhandl]

@handrews How about renaming the new section to just "Case Sensitivity"? That would draw more attention, and we still can cover HTTP in the unchanged section text?

OpenAPI-Specification/versions/3.0.4.md

Lines 62 to 65 in b7c20ee

	### HTTP and Case Sensitivity
	As most field names and values in the OpenAPI Specification are case-sensitive, this document endeavors to call out any case-insensitive names and values.
	However, the case sensitivity of field names and values that map directly to HTTP concepts follow the case sensitivity rules of HTTP, even if this document does not make a note of every concept.

I'll add that as a proposal to #4001

[ralfhandl]

@rvedotrc If this new section also covers your concern, then please close this PR.

[handrews]

@ralfhandl I'd support that rename!