M3's Comprehensive Search tool allows you to find images based on name, attributes, and expressions.  It's search stack buttons, shown below, allow you to combine results of multiple searches.  This section describes the use of these buttons. 

The components of the Search Stack bar are: 

Perform 
Once you have entered your search criteria, press this button to perform the search  operation. 

View (left)
Press this button to view the search results in an Advanced Browser.

>P, <P, >S, <S 
These buttons let you push or pop search results or refined results onto two stacks.  (Known as primary and secondary) 

Add, Sub, And, Dif 
These buttons let you perform operations between the search results (on the left) and the refined results. (on the right)  The operations they perform are: 
  Add - Adds non duplicate files from left to right. 
  Sub - Removes files which are common to both results from the right. 
  And - Only keeps the images which are common to both search results in right. 
  Dif - Replaces right with images which are in left and not right. 

Clear
Clears the refined results.  A cleared result has 0 files in it.

View (right)
Press this button to view the refined results in an Advanced Browser.

An example use of buttons:

Search: All images which are of people, sad or happy but not both.

1. Enter search items DB:\*, [X] People, [X] Happy, [ ] Sad
2. Perform search
3. Press Add to move result to the right.
4. Modify search items to DB:\*, [X] People, [ ] Happy, [X] Sad
5. Perform search
6. Press Add to add results to the right
7. Press the right View to view results.