Function query_selector 

pub fn query_selector<E, Q>(
    root: E::ConcreteNode,
    selector_list: &SelectorList<E::Impl>,
    results: &mut Q::Output,
    may_use_invalidation: MayUseInvalidation,
)
where
    E: TElement,
    Q: SelectorQuery<E>,

https://dom.spec.whatwg.org/#dom-parentnode-queryselector