`Keyword` is imported from dir-spec and ``` KeyValue ::= Keyword "=" Value Keyword = KeywordChar+ KeywordChar ::= 'A' ... 'Z' | 'a' ... 'z' | '0' ... '9' | '-' ``` but... most headers have underscores in them. My parser wasn't strict enough to catch this the first time. ): I suggest this is fixed with a specification update to reflect reality rather than creating complexity we have to maintain forever parsing two sets of keys.