This is a utility function for determining whether a specified
Unicode character is a hexadecimal digit as defined in RFC 2396;
that is, one of the ASCII characters 0-9, a-f, or A-F.
This is a utility function for determining whether a specified character
is a combining character according to production 87
of the XML 1.0 specification.
This is a utility function for determining whether a specified
character is a letter or digit according to productions 84 and 88
of the XML 1.0 specification.
This is a utility function for determining whether a specified
character is a legal name start character according to production 5
of the XML 1.0 specification.
This is a utility function for determining whether a specified
Unicode character is a whitespace character according to production 3
of the XML 1.0 specification.