Thats the merge section to bring the dpr selector in the bottom right of the 'actions' tab.. this is the merge for the 'floating character sheet tabs' extensions that brings all the character sheet tab pages into individual windows. Its the merge for that extension window... If you dont have the extension this will show up, if you have the extension it will merge.
Is not possible, as far as I know, to xml merge into the class for a supported extension and special case this code merge in/out depending on if the extension is loaded or not....
Its ok to have that warning, and nothing I can do to stop it.
If you have this extension enabled it should go away, as it will correctly merge with this.
Floating tabs extension
-pete