def xml(self, attribs = None,elements = None, skipchildren = False):
        """See :meth:`AbstractElement.xml`"""
        if not attribs: attribs = {}
        E = ElementMaker(namespace="http://ilk.uvt.nl/folia",nsmap={None: "http://ilk.uvt.nl/folia", 'xml' : "http://www.w3.org/XML/1998/namespace"})
        e = super(AbstractSpanAnnotation,self).xml(attribs, elements, True)
        for child in self:
            if isinstance(child, (Word, Morpheme, Phoneme)):
                #Include REFERENCES to word items instead of word items themselves
                attribs['{' + NSFOLIA + '}id'] = child.id
                if child.PRINTABLE and child.hastext(self.textclass):
                    attribs['{' + NSFOLIA + '}t'] = child.text(self.textclass)
                e.append( E.wref(**attribs) )
            elif not (isinstance(child, Feature) and child.SUBSET): #Don't add pre-defined features, they are already added as attributes
                e.append( child.xml() )
        return e
See :meth:`AbstractElement.xml`