Here is a list of all documented struct and union fields with links to the struct/union documentation for each field:

debug : ubjs_parser_settings
error : ubjs_parser_context
free : ubjs_parser_context , ubjs_writer_context
limit_bytes_since_last_callback : ubjs_parser_settings
limit_container_length : ubjs_parser_settings
limit_recursion_level : ubjs_parser_settings
limit_string_length : ubjs_parser_settings
parsed : ubjs_parser_context
userdata : ubjs_parser_context , ubjs_writer_context
would_print : ubjs_writer_context
would_write : ubjs_writer_context