Select matches
Select all items that are also listed in the other pane.
Select uniques
Select all items that are only listed in this pane.
Select newer
Select all matches with a more recent modified date.
Select different
Select all matches with a different size or modified date.
Select uniques and newer
Select all items that are unique or newer.
Select uniques and different
Select all items that are unique or different.
Select selected
Select all items that are selected in the other pane.

Ignore file extensions