Function registry_index 

pub fn registry_index(
    version: Version,
    registry_id: &str,
    entry_id: &str,
) -> Option<i32>

Returns the index of entry_id within registry_id for version, which is the numeric ID the client uses on the wire (e.g. in chunk biome palettes, dimension types in the Login packet). Returns None if the registry or entry isn’t shipped.