+ // XXX Note that this code is not strictly correct: we
+ // do a case-insensitive match in
+ // LanguageConverter::getHeaderVariant() while the
+ // (abandoned, draft) spec for the `Key` header only
+ // allows case-sensitive matches. To match the logic
+ // in LanguageConverter::getHeaderVariant() we should
+ // also be looking at fallback variants and deprecated
+ // mediawiki-internal codes, as well as BCP 47
+ // normalized forms.
+