We discovered an undocumented behaviour with the OnTimer script trigger.
One of our solution scripts executes the Install OnTimer Script script step on a document window. At a later time, a user action causes the creation of a card window.
Testing revealed a bug. We forgot that new windows inherit the original window's OnTimer Script. It did weird things when it fired in the context of the card window. We fixed this error, but found an unexpected behaviour in the process of debugging.
The Install OnTimer Script topic of the Claris FileMaker Pro 19 Help points to another topic, About window styles. The latter mentions OnTimer scripts only once, in the Dialog window section. It states:
… OnTimer scripts do not execute when a dialog window is open unless the script launches from the dialog window itself.
We took this to mean that script triggers fire for parent windows of card windows because the Card section makes no mention of OnTimer scripts.
Not quite! The OnTimer script fires only when the card window is closed (and, of course, all scripts are done running). It forced us to rethink our use of the OnTimer script big time.
Here's hoping this observation saves you some time.