Function new_body_handler_id 

pub fn new_body_handler_id(prefix: &str) -> String

The name one plugin instance keeps its response body handler under.

The handlers of a request are kept by name, and the name used to be the plugin’s category. Two plugins of one category on a location then shared a single slot: the second replaced the handler of the first, and both ran the one that was left, so its rules were applied twice and the other’s not at all.