fn parse_at_rule<'i, P, E>(
start: &ParserState,
name: CowRcStr<'i>,
input: &mut Parser<'i>,
parser: &mut P,
) -> Result<<P as AtRuleParser<'i>>::AtRule, (ParseError<E>, &'i str, SourceLocation)>where
P: AtRuleParser<'i, Error = E>,