DTD for D-Bus Introspection data (C) 2005-02-02 David A. Wheeler; released under the D-Bus licenses, GNU GPL version 2 (or greater) and AFL 1.1 (or greater) see D-Bus specification for documentation Method arguments SHOULD include "direction", while signal and error arguments SHOULD not (since there's no point). The DTD format can't express that subtlety. Generic metadata AKA "attribute"