Function remove_keyed 

pub fn remove_keyed(
    root: &mut Value,
    prefix: &str,
    slug: &str,
    keyed_lists: &[KeyedList<'_>],
) -> DocumentResult<usize>

Remove the unique element named by slug and return its former index.

The index lets a source-preserving backend remove the exact same element from its syntax tree without independently repeating the identity lookup.