It occurs to me (after mentioning collation order, in a different part of this thread, as one reason that we would want to distinguish scripts) that it might be

It occurs to me (after mentioning collation order, in a different part of this thread, as one reason that we would want to distinguish scripts) that it might be unclear even for collation purposes when scripts are or are not distinct, especially for Cyrillic, Latin, and Arabic scripts which are used to write many different languages which have often added their own extensions. I guess the official answer is "attempt to distinguish everything that any language is known to distinguish, and then use locales to implement different collation orders by language", or something like that? But it's still not totally obvious how one could make a principled decision about, say, whether the encoding of Persian and Urdu writing (obviously including their extensions) should be unified with the encoding of Arabic writing. One could argue that Nastaliq is like a "font"... or not...