A suggestion that I've thought about from time to time:

If an attribute in XSLT expects an expression or an AVT, then a leading
undoubled "}" in the attribute value indicates that is to be treated as a
plain string.

So for an expression

<xsl:param name="x" select="}O'Reilly"/>

indicates that the default value is the string "O'Reilly"

and in an AVT

regex="}[a-z]{4}"

indicates that the regex is [a-z]{4}

This relies on the fact that neither an AVT nor an expression can legally
begin with an undoubled "}", nor is it ever likely to. And you can think of
"}" as meaning "exit expression mode, here is plain text".

Nice idea, or just too quirky?

Michael Kay
Saxonica