Function parse_qualified_rule 

fn parse_qualified_rule<'i, P, E>(
    start: &ParserState,
    input: &mut Parser<'i>,
    parser: &mut P,
    nested: bool,
) -> Result<<P as QualifiedRuleParser<'i>>::QualifiedRule, ParseError<E>>
where
    P: QualifiedRuleParser<'i, Error = E>,