Minor Description
When TabbedPanel is added as a sub-panel of ListPanel,
ListPanel will output duplicated IDs.
<div id="listPanel">
<div id="tabbedPanel">
<div id="tabbedPanel"></div>
</div>
</div>
As a simple solution, I'd like to introduce a marker interface that shows
whether a sub-panel will output the div element with the id attribute.
- Perhaps the name of interface may not be appropriate.
For more detail, please see a patch.