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"