'Add or modify a <query> element.
Query elements are differentiated by their namespace.
Arguments:
value -- The namespace of the <query> element.'

def set_query(self, value):

    query = self.xml.find(('{%s}query' % value))
    if ((query is None) and value):
        plugin = self.plugin_tag_map.get(('{%s}query' % value), None)
        if plugin:
            self.enable(plugin.plugin_attrib)
        else:
            self.clear()
            query = ET.Element(('{%s}query' % value))
            self.xml.append(query)
    return self
