Chenge the Category Field instance on a Layout to a Checkbox.
Google "checkbox site:filemaker.com"
Google "checkbox site:forums.filemaker.com"
Custom Google Search for Filemaker
Search for checkbox
When you turn a checkbox from OFF to ON, the value corresponding to that checkbox is ADDED to the end of that field.
When you turn a checkbox from ON to OFF, the value corresponding to that checkbox is REMOVED from the field.
(This behavior is the same in a related table or in the same table)
Example: Suppose the text field "Color" has the value list "[ ] Red [ ] Green [ ] Orange"
This is how the information is stored:
Click on Red --> Color contains "Red"
Click on Green --> Color contains "Red¶Green"
Click off Red --> Color contains "Green"
Click on Red --> Color contains "Green¶Red"
Click on Orange --> Color contains "Green¶Red¶Orange"