specificityOfSelector function
The specificity of one selector, given as source text.
Returns CssSpecificity.zero for text csslib cannot read as a selector.
Implementation
CssSpecificity specificityOfSelector(String selector) {
final errors = <cssparser.Message>[];
final group = cssparser.parseSelectorGroup(selector, errors: errors);
if (group == null || group.selectors.isEmpty) return CssSpecificity.zero;
return _specificityOfSelector(group.selectors.first);
}