Function lineage_keys 

pub fn lineage_keys(
    document: &Value,
    identity: &str,
    canonicalize: &dyn Fn(&str) -> String,
) -> BTreeSet<String>

The lineage keys of a part: its own source identity, every identity it was saved from (derivedFrom) and its family (family:<file>), each passed through canonicalize (stores spell one file several ways). Two parts share lineage when their key sets intersect.