@Ralf – are you aware, that you posted your question in the "InDesign Scripting" forum?
If yes and you want to script what Alec is showing in his answer, I give you the following hint:
look after inserted labels (inserted by the "insertLabel()" function in JavaScript). All properties of the scrollable frame are attached by the "Overlay Creator" plug-in, if you use it in the UI.
If you used the Overlay Creator feature "Scrollable Frame" on your rectangle and export that to an IDMS file, you could inspect and extract all the key/value pairs necessary from that file to mimic the Overlay Creator by scripting the key/value pairs.
Uwe
