I'm not sure I understand the use case for making the second argument of string-join into a sequence.

I'm not sure I understand the use case for making the second argument of string-join into a sequence.

It’s an alignment with intersperse/join; and I did not see a reason not to do it, as we already allow it to be an empty sequence.

fn:chain-sequence() as an alternative name for fn:join() ?

I have done the following changes (Sorry for the repeated commits):

• fn:string-join: reverted to accept at most one separator item.
• fn:join: renamed to fn:sequence-join, mandatory separator argument.
• array:join: Signature and equivalent XPath code changed to take charge of empty-sequence separators (thanks Reece).