Add OPTIONAL to conformace section

[awoie]

OPTIONAL is a normative word, but we were using the lowercase version of it (on purpose). We could also fix things by just using "OPTIONAL", as that's equivalent to "MAY".

@msporny According to the Conformance section, we only have the following:

The key words MAY, MUST, MUST NOT, RECOMMENDED, SHOULD, and SHOULD NOT in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

I know that OPTIONAL is used in IETF RFCs but I couldn't find it in the paragraph above. Should we add OPTIONAL there too? Or what is the reason it was not added?

Originally posted by @awoie in #1181 (comment)

[msporny]

I know that OPTIONAL is used in IETF RFCs but I couldn't find it in the paragraph above. Should we add OPTIONAL there too? Or what is the reason it was not added?

That paragraph is auto-generated by ReSpec based on the normative RFC language used throughout the document. So, if you don't use a certain RFC term, it's not added to that paragraph. If we use "OPTIONAL" (in all caps) in the document, ReSpec will modify that paragraph I pointed to and will add the word automatically to that paragraph.

So, no reason to modify that particular paragraph, it'll auto-update if we use the OPTIONAL language in the places where we use lowercase "optional" today.

We should close this issue given that ReSpec auto-generates that paragraph, will do the right thing if we add the OPTIONAL RFC language anywhere in the spec, (and we have no control over that paragraph).

[awoie]

Closing issue based on @msporny reply.