.ZUL File Extension
What is a ZUL file?
Web file created in the ZK User Interface Markup Language (ZUML), an XML-based language supported by Ajax technology and Java classes; contains definitions for user interface elements as well as zscript code.
ZUL files are used to create rich Web-based user interfaces. Their contents are first parsed on a Java-based Web server, such as Apache Tomcat, and then sent to the requesting client Web browser.
Conceptually, ZUL files are similar to .JSP files.