Function topic_leaf 

pub fn topic_leaf(key: &str) -> &str

The leaf (entity) segment of a record key — the trailing component after the last separator. Both . and / are treated as delimiters, since keys use either convention (temp.vienna or sensors/temp/vienna), and both yield vienna. Servers report this as a record’s entity, which identifies the node only where the leaf is the node: station.17.temperature yields temperature, not 17.