Some languages use »this syntax« for quotes, some „this“, and many more many different kinds. Plus, there are many other kinds of delimiters, so the specification is discriminating against languages the creators didn’t think of, and violating the principle of least surprise for users of these languages.
If you don’t believe me, look here: https://secure.wikimedia.org/wikipedia/de/wiki/Anf%C3%BChrungszeichen#Andere_Sprachen
even if you don’t know german, you should understand the table. And that’s only quotation marks!
Proposal: Specify that only “punctuation” may be before start-strings and after end-strings, allowing the implementation to choose what’s punctuation. (hint: nobody will want to use a list of ten or twenty symbols) That makes the spec easier and i can’t think of a single case where somebody might want to make punctuation invalidate interpretting of roles. and if there are some, the user can still \-escape the start-string, as he can already.