It is not as simple as modifying a single line in the script.
If you don't already know what to do based on the above, it is probably too hard for you to try.
You would have to modify a macro called from the Master Script of the Window Marker. Yu would probably have to create new parameters so you can decide whether you want to display the Sill or the Head. If the choice is the Head, its value would have to be calculated.
Also, the Interface Script of the Element would have to be modified so that the custom interface also displays the Head option.
So this is several hours of work, even if you know GDL.
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