<html xmlns:tal="http://xml.zope.org/namespaces/tal"> <p tal:replace="structure string:<a>bar</a>" tal:attributes="href string:http://www.python.org">dummy text</p> <p tal:define="x python:1" tal:on-error="string:bad boy!"> <span tal:define="x python:2"> <span tal:define="x python:3"> <span tal:content="python:1/0"/> </span> </span> </p> <p tal:on-error="string:x undefined"> <span tal:content="x"/> </p> </html>