The <ui:debug> tag (ComponentHandler) defines a debug component in the component tree that is capable of capturing debugging information such as component tree, scoped variables, and view state. For example, you can add the <ui:debug> tag into a template using the following code:

<ui:debug hotkey="q" rendered="true"/>

Now, when you press Ctrl + Shift + Q, you will see something like the following screenshot:

The complete application is named ch12_9. The <ui:debug> tag was added in layout.xhtml.