Bug fix:

1) Bug fix for the class with name ".mg0px { ... }".
$css = preg_replace('/(^|[^0-9]):(?:0?\.)?0(?:em|ex|ch|rem|vw|vh|vm|vmin|cm|mm|in|px|pt|pc|%|deg|g?rad|m?s|k?hz)/iS', '${1}:0', $css);

2) Bug fix unclosed quotes in filter. Example: progid:DXImageTransform.Microsoft.gradient(startColorstr='u', endColorstr='url(___YUICSSMIN_PRESERVED_TOKEN_0___);
$css = preg_replace_callback('/(?:"(?:[^\\\\";}]|\\\\.|\\\\)*")|'."(?:'(?:[^\\\\';}]|\\\\.|\\\\)*')/S", array($this, 'replace_string'), $css);