Suppose that there is a Work Panel with a subfile and a column used to mark and unmark the subfile rows. This column will be the variable &Op character with length 1.
We want the character of the check to appear in &Op when the user marks a row.
In the event start of the Work Panel the font is changed from &Op to "Monotype Sorts":
Event Start
&Op.FontName = 'Monotype Sorts'
EndEvent
And then:
Event &Op.Click
If &Op = '4'
&Op = ' '
Else
&Op = '4'
Endif
EndEvent
Where "4" in "Monotype Sorts" is a check.
There are also other characters, for example, the character "7" is a cross, "10" is a pencil, etc.