Liferay 6 supports ZK5. I tried to deploy some old portlets we developed with ZK3 without success, Buttons rendered in a terrible way.
To support the portlet configuration mode, he supports block of your portlet.xml file should look like:
1<supports>
2 <mime-type>text/html</mime-type>
3 <portlet-mode>EDIT</portlet-mode>
4</supports>
You will also have to define an init-param for editing.
For more documentation check the ZK site and its forum at http://www.zkoss.org
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