Selection Assistant

To bring up the selection assistant menu, clicking on the Selection Assistant button in the Duplicate Files Tab.
Selection Assistant
1

Mark

1. Mark
 
Brings up the marking actions available.
2

Select by Location...

2. Select by Location...
Brings up the Select by Location window.
3

Select by text pattern...

3. Select by text pattern...
Brings up the Select by Text Pattern window.
 
4

Groups with all files marked...

4. Groups with all files marked...
Marking all the files in group may lead to all copies of a file being deleted. This helps prevent that by bringing up a list of any groups which have had all the files marked for removal.  Selecting a group number and clicking 'Jump to Group' or double clicking will jump to the group in the list view.
5

Unmark All

5. Unmark All
Removes all the marks on the files.
6

Work only on currently selected rows (option)

6. Work only on currently selected rows (option)
When checked, Selection Assistant operations will only affect the rows selected (highlighted) in the duplicate files list.
Note, this currently excludes 'Select by Location' operations.
7

Leave existing marks unchanged (option)

7. Leave existing marks unchanged (option)
Selection assistant operations will usually clear existing marks.  This prevents that.