'Return the names of all stanza interfaces provided by the
stanza object.
Allows stanza objects to be used like dictionaries.'

def keys(self):

    out = []
    out += [x for x in self.interfaces]
    out += [x for x in self.loaded_plugins]
    out.append(u'lang')
    if self.iterables:
        out.append(u'substanzas')
    return out
