Function insert_an_element_at_the_adjusted_insertion_location 

fn insert_an_element_at_the_adjusted_insertion_location(
    cx: &mut JSContext,
    node_to_insert: Dom<Node>,
    adjusted_insertion_location_parent: &Node,
    adjusted_insertion_location_child: Option<&Node>,
    parsing_algorithm: ParsingAlgorithm,
    custom_element_reaction_stack: &CustomElementReactionStack,
)

https://html.spec.whatwg.org/multipage/#insert-an-element-at-the-adjusted-insertion-location