Property:

org.zkoss.zk.ZUML.cache

Default: true

Specifies whether to cache the result of ZK ZUML files (the *.zul files in the classpath loaded by ZumlExtendlet) at the server. By default, it is enabled. It means the ZUML code specified in a zul file is loaded and cached at the server. The performance is good. However, if you are debugging the ZUML code and you’d like to modify the content without restarting the server, you could disable the caching of ZUML files.