Bug: Validator allows pseudo-elements on invalid places

Hi,

  The following ruleset is invalid

    a.foo:before:hover { color: red }

because the pseudo-element ::before must occur only after a sequence of
simple collectors, thus 

    a.foo:hover:before { color: red }

would be valid. The Validator does not complain about the error and even
worse it repairs the error in the pretty printer, converting 

    a.foo:before:hover { color: red } /* to */
    a.foo:hover:before { color: red }

regards.