HTML 5 classnames and IDs

Question

I know that in HTML4 classes and id cannot start with numbers.

I am coding in HTML 5/php and alot of my ids and classes have just numbers in them that point to a pri

Answer 1

The official html5 specs are here: id-attribute in html5.

(Here you go for html4)

So in html5 the only restriction is minimum 1 char and no whitespaces.