XSLT 1.1: working with strings (replace)

Since there are functions like translate why don't you include a
function replace that would work with regular expressions.

Even for simple cases translate is so limited. For instance,
I cannot translate a single character into a sequence of 2
characters (like an "escape" sequence).

I would also like to have split/join functions but I don't know
exactly how it could be done, maybe with a node set of text nodes.

Regards,
Ricardo Amador