NCNAME_PATTERN

NCNAME_PATTERN = '[A-Za-z_][A-Za-z0-9\\.\\-_]*'

A regex for prefixes, from https://www.w3.org/TR/1999/REC-xml-names-19990114/#NT-NCName.

prefix := NCName
NCName := (Letter | '_') (NCNameChar)*
NCNameChar  ::=     Letter | Digit | '.' | '-' | '_'