all_fields Iterates over all paths in form a.b[0].c[1] in alphabetical order
and their corresponding values. all_fields_non_object_root An iterator with a single “message” element all_fields_skip_array_elements An iterator similar to all_fields, but instead of visiting each array element individually,
it treats the entire array as a single value. all_fields_unquoted Iterates over all paths in form a.b[0].c[1] in alphabetical order and their corresponding
values. Field names containing meta-characters are not quoted. all_metadata_fields Same functionality as all_fields but it prepends a character that denotes the
path type. keys Iterates over all paths in form a.b[0].c[1] in alphabetical order.
It is implemented as a wrapper around all_fields to reduce code
duplication.