Author names: Valid Unicode is required, and for non-ASCII names, an ASCII-only identifier is required.
Bibliographic text: The reference entry must be in English; whatever subfields are present MUST be available in ASCII. As long as good sense is used, they MAY also include non-ASCII characters at author discretion. This applies to both normative and informative references.
Keywords: US-ASCII only
Body: The mention of non-ASCII characters requires Unicode code points, encourage characters, allow Unicode character names. General use does not require any clarifying identifiers or Unicode names. (Note: use versus mention distinction)
We would NOT apply in the use case and we WOULD apply in the mention case. So, CATEGORY NUMBER naïve 300 but CATEGORY EXAMPLES Latin naïve (U+0063 U+0061 U+00EF U+0076 U+0065)
Tables: Tables follow the same rules for identifiers and characters as the body. If it is sensible (i.e., more understandable for a reader) for a given document to have two tables, one including the identifiers and characters, one with just the characters, that will be allowed on a case by case basis.
U+ notation must be used except within a code component where you must follow the rules of the programming language in which you are writing the code
Normalization forms: If the normalization matters to the content, the authors must submit in a normalization-resistant form. Do not expect normalization forms to be preserved.
Codepoint numbers ("U+0394") and Unicode character names ("Greek Capital Letter Delta") are normalization-resistant forms. The characters themselves may not be.
All documents should identify themselves as being UTF-8. Both the canonical XML format and the non-canonical HTML format must contain metadata that specifies that the encoding is UTF-8. The non-canonical text-only format must begin with a UTF-8 BOM.
An implementer must be able to implement the specification without any confusion or ambiguity introduced by the use of UTF-8 rather than ASCII.
People must be able to reference (cite) the RFC from elsewhere in a standard way, including from documents that only support ASCII.
The RFC must be able to reference (cite) other documents in an unambiguous way.
Cross-references (including references to other documents) must be unambiguous even from a printed document.
Tools must be able to index the RFC in various ways, so searching for keywords, author names, and so on can work.