I do this in two different pop-ups in my Known Bugs List database. Here's the download link. Feel free to take a look at the scripts attached to "Find" or "New" on the first screen.
Both manage the window resize steps dynamically (and check to see if this is a windows platform as this change is a windows issue that you don't have with Macs.) and use an infinite loop to keep the window in a "modal" state where the user must dismiss this window before returning to the main window.
Feel free to ask questions if some part of the scripts don't make sense to you.
Just a tip. Whenver you add these Loop/pause steps for a "modal" window, be sure you have a button on the layout of the little window, with the option "Halt" current scripts (in the Button dialog). Otherwise you can get stuck in an endless loop, and have to Force Quit FileMaker, which can damage the file.
Thanks, Fenton. That's twice now that I've forgotten that key detail. It's implemented in the file, but it should always be made clear when this technique is described.
My you re-post your download link? I cannot find it form your pervious post. Thank you.
Sorry, I usually include that, must have forgotten that step:
Click the Blue download button with the white arrow. The green button downloads an application that has nothing to do with this file.