https://gcc.gnu.org/bugzilla/show_bug.cgi?id=33167
--- Comment #7 from joseph at codesourcery dot com <joseph at codesourcery dot com> --- "longest sequence of characters that can constitute the escape sequence" resolves an ambiguity between alternative parses permitted by the syntax; it doesn't need to deal with anything that is not permitted by the syntax. Four or more octal characters in an octal sequence are not a parse permitted by the syntax, whereas more than two hex characters in a hex sequence are a parse permitted by the syntax.
