inbetween

Taken from http://www.w3.org/TR/2004/REC-xml-20040204/

Names and Tokens
[4]   	NameChar   ::=   	Letter | Digit | '.' | '-' | '_' | ':' | CombiningChar | Extender
[5]   	Name	   ::=   	(Letter | '_' | ':') (NameChar)*
...

Name and ID attributes begin with a letter, underscore, or colon, which is followed by any combination of letters, digits, period, dash, underscore colon, or combining characters. "CombiningChar" comes from a list of unicode characters.