XPages Custom controls parameter definitions

One of the very cool features in XPages is the ability to create your own custom controls. While on the first look one could say "well, they are just subforms with a new name" the second look shows bigger differences:

• Custom controls can appear more than once on a page, subforms only once (yes there was the possibility to add a subform twice if it didn't contain any fields, but that was not intended)
• Custom controls are self aware: they "know" what is inside and what is outside
• Custom controls have parameters. You can define parameters that the custom control will address as CompositeData.[parameterName] and the hosting pages address as [controlName].[parameterName]

When you look at the source code of a page you can clearly see the parameters you might have set for a custom control. However when you look at the source code of your custom control, you won't see any definition. Puzzled me for a moment, so I asked the master. At the very end XPages is a JFS application. In JFS a custom control has 2 files (at least): the code and the definition. XPages shields you from the complexity by allowing you to edit everything in one UI. But if you *really* want to have a look, add the Navigator window to your Domino Designer perspective and navigate to the custom control directory. Here you will find MyControl.xsp as well as MyControl.xsp-config. If you want to understand what the containing XML is all about, take a peek at a JSF tutorial