Can XHTML and HTML class attributes value start with a number?

Question

Can XHTML and HTML class attributes value start with a number?

Answer 1

No, they cannot. They must begin with a letter. Some browsers may erroneously support them, though.

EDIT: You can start off with unicode escape points and specify the code for a number.

EDIT #2: Test case http://work.arounds.org/sandbox/66/run