It looks like ':' is supported by XML ID type. According to XML 1.0 specification, section 3.3.1, Attribute Types:
http://www.w3.org/TR/2004/REC-xml-20040204/#sec-attribute-types the validity constraint for ID type, must follow the XML Name production: [5] Name ::= (Letter | '_' | ':') (NameChar)* which includes colon as a legal character. Kind Regards, John Fallows.
