'Mark an interest in a PEP subscription by including a disco
feature with the \'+notify\' extension.
Arguments:
namespace -- The base namespace to register as an interest, such
as \'http://jabber.org/protocol/tune\'. This may also
be a list of such namespaces.
jid       -- Optionally specify the JID.'

def add_interest(self, namespace, jid=None):

    if ((not isinstance(namespace, set)) and (not isinstance(namespace, list))):
        namespace = [namespace]
    for ns in namespace:
        self.xmpp['xep_0030'].add_feature(('%s+notify' % ns), jid=jid)
    self.xmpp['xep_0115'].update_caps(jid)
