'Convert to XML
:return: Generated TwiML'

def xml(self):

    el = ET.Element(self.name)
    keys = self.attrs.keys()
    keys = sorted(keys)
    for a in keys:
        value = self.attrs[a]
        if isinstance(value, bool):
            el.set(a, str(value).lower())
        else:
            el.set(a, str(value))
    if self.value:
        el.text = self.value
    for verb in self.verbs:
        el.append(verb.xml())
    return el
