When developing an XPages Custom Control you may encounter the issue:



If your custom control contains only a single control that is one of these tags:
xp:viewColumn, xp:column, xp:eventHandler, xp:selectItem, xp:selectItems
then the compositeData is not available in "Compute Dynamically" bindings,
only in "Compute on Page Load" bindings.

Normally when a custom control is inserted into an XPage, it leaves a panel-like control
in the control tree, the UIIncludeComposite. That panel provides functionality:

• it publishes the compositeData to be available in compute dynamically bindings
• it publishes any data sources that were defined on the root of the custom control page,
  and handles the other data-related properties (readonly, acl etc)
• it provides a clientId naming scope.
So if you have a custom control containing ,
and an outer page containing:
<xp:myCustom>
<xp:myCustom>
it ensures the 2 divs have different ids in the HTML source:
<div id="view:_id1:_id2:div1"></div>
<div id="view:_id1:_id3:div1"></div>
(the first custom control panel is _id2, and the 2nd custom control panel is _id3)