Function store_entries 

pub(crate) fn store_entries(
    extra: &[(Value, Value)],
    writes_key: impl Fn(&str) -> bool,
) -> Vec<(Value, Value)>

The store entries to write after a map’s own keys.

written_entries with one pass in front of it: an entry naming a key the map writes from a field is dropped, because the field wins and writing both would put that key in the map twice.