An XML name may start with a letter, underscore or colon. However the colon is reserved for use with namespaces and is not fully standardized as of XML version 1.
Subsequent characters in the name may be any one of:
Dot (period/full stop)
Dash (minus sign)
Your name values should not begin with the string "XML" or any sequence of characters that might degenerate to it after case conversion or international character substitution.
Combining characters and Extenders are enumerated in Appendix B of the XML version 1.0 standard.