Select Box in window.open

FlensGold

Hello,
I am new to this forum just as I am new to NAV as well.
I am familiar with coding, thats not the point, but sometimes NAV works a bit different then I expected.

Right now I have a form where the user can enter several information. Behind one field I would like to open a window (triggered in "OnAfterValidate") if the user enters specific information. In that case this "Popup" Window should include a select Box offering the user 3 options. How can I handle this in NAV? Using window.open creates such a popup window.
If I would use window.input the user could enter information, but that is not what I am looking for. I would like to offer him 3 options and then continue with the selection.
I would appreciate any help. I already tried the search and google, but I assume I used the wrong search parameter?
Kind regards

Edit:
After posting this I tested around and found out, that I was on the wrong path.
I assume the correct way should be the DIALOG.STRMENU.
I achieved in getting the Select Box, just trying to deal with the result

Edit 2:
Got it, just for completion:

Options := 'A,B,C,D';
// Sets the default to option 3
Selected := Dialog.STRMENU(Options, 3, 'Please choose:');
MESSAGE('You selected option', Selected);