Initial index.zul file does not include name space definition of ZK,
so code completion does not work.
If you create new zul file using next step:
Web page–>Right Click–>new –>ZKProject zkCanvas,
then the newly created zul file looks like below.
####################################
<?xml version="1.0" encoding="UTF-8"?>
<zk xmlns="http://www.zkoss.org/2005/zul">
</zk>
####################################
With this newly created zul file(with schema:xmlns=”http://www.zkoss.org/2005/zul”),
code completion works fine.