':return: list of xml descriptions for rolesets.'

def rolesets(self, baseform=None):

    if (baseform is not None):
        framefile = (u'frames/%s.xml' % baseform)
        if (framefile not in self._framefiles):
            raise ValueError((u'Frameset    file    for    %s    not    found' % baseform))
        framefiles = [framefile]
    else:
        framefiles = self._framefiles
    rsets = []
    for framefile in framefiles:
        etree = ElementTree.parse(self.abspath(framefile).open()).getroot()
        rsets.append(etree.findall(u'predicate/roleset'))
    return LazyConcatenation(rsets)
