Applies a function to every key of a term, however deeply nested — through maps, lists and MapSets; any other term passes through unchanged.

Dowser.Client.Decoder is the pass dowser_client runs itself from :keys/:decoder; this protocol casts a whole term's keys in one go, for a backend package that needs to do it on its own:

Dowser.CoreExt.Keyable.transform_keys(body, &String.to_existing_atom/1)

String.to_atom/1 grows the atom table for every key a backend ever returns, so prefer String.to_existing_atom/1 on anything attacker- or mapping-driven.