[basex-talk] XML name characters and regexes with multi-character escapes?

Recently I had occasion to test a string to see whether it is an NCName. I typed something like:

matches("foo","\i\c*")

But instead of the value 'true', I got an error message saying that '\i\c*' is an invalid regular expression. I believe it is a valid regular expression and that \i and \c are defined as multi-character escapes in XSD. Other multi-character escapes (., \s, ...) seem to be supported.

Am I missing something? Since \i and \c vary for different versions of XML, perhaps BaseX is expecting me to tell it which version of XML I want to be using for them?

I'm currently using 6.5.1 and have not checked against the current version of BaseX, but I don't see anything about regular expressions in the change logs.