With ZK-2957 client-attributes are enabled on xhtml elements.
As the current implementation only assumes self closing tags, xhtml elements with children are not handled properly causing corrupted html output and JS errors.

The attachment reproduces this case.

the problem occurs here:
https://github.com/zkoss/zk/blob/v8.0.2.1/zk/src/archive/web/js/zk/widget.js#L5329