def to_xml(self, lvl=0, indent='  '):
        spaces = indent * lvl
        data = spaces + '<RhetRel name="' + self.relation + '">\n'
        data += indent + spaces + '<marker>' + self.marker + '</marker>\n'
        data += indent + spaces + '<nuclei>\n'
        data += indent * 2 + spaces + '<nucleus>\n'
        for n in self.nuclei:
            data += n.to_xml(lvl + 3) + '\n'
        data += indent * 2 + spaces + '</nucleus>\n'
        data += indent * 2 + spaces + '<satellite>\n'
        data += self.satellite.to_xml(lvl + 3)
        data += indent * 2 + spaces + '</satellite>\n'
        data += spaces + '</RhetRel>\n'
        return data