What is a ZUL file?
A file with .zul extension is a web file created with the User Interface Markup Language (ZUML) and contains definitions for user interface elements. Ajax and Java classes support using the XML-based ZUML for developing server side files. ZUL file format was developed by ZK, a UI framework that enables you to build web and mobile applications without the knowledge of JavaScript or AJAX.
ZUL File Format
ZUL files are XML-based, consisting of different elements to construct user interface. The ZK loader uses each XML element to create a component. The overall processing of the page elements such as page title, description, etc. are described by each XML processing instruction of ZUML.
ZUL Example
In the following example of ZUML code, the first line specifies the page title, the second line creates a root component with title and border, and the third line creates a button with label and an event listener.
<?page title="Super Application"?>
<window title="Super Hello" border="normal">
<button label="hi" onClick='alert("hi")'/>
The ZUL schema can be downloaded from http://www.zkoss.org/2005/zul/zul.xsd.