Except that the validators themselves are so positively anal,
when they flag an error or warning whenever a -moz- or -webkit or -o- i.e. a browser specific qualification term is used.
also they want you to specify 0px rather than 0 or other units
Zero is Zero whatever units the validator wants to check it against!
just try validating the WordPress twentyeleven style.css it throws 140 odd errors which are all of the nature above or the validator is recovering from parse errors
The validators are useless if you cannot sort the wheat from the chaff!!!
We need validators that recognise browser specific qualification terms!
