How to check if string is a valid XML element name?

Question

I need a regex or a function in PHP that will validate a string to be a good XML element name.

Form w3schools:

XML elements must follow these

Answer 1

This should give you roughly what you need [Assuming you are using Unicode]:
(Note: This is completely untested.)

[^\p{P}xX0-9][^mMlL\s]{2}[\w\p{P}0-9-]

\p{P} is the syntax for Unicode Punctuation marks in PHP's regular expression syntax.