Hi Dan, thanks so much for your time.
I spent a bit of time trying to get this up and running but can’t seem to work it out. It’s throwing the error: TypeError: thisLayer(…).property is not a function It says the error is at line 1. But I grabbed the line 1 code and used it by itself in another expression to test, and it does not throw an error, leaving me baffled.
Here’s a screenshot of the error:

And a screenshot of where that first line is actually working fine in this other expression:

Searching web for the error returns another thread here on Creative Cow where you commented “I think the new JavaScript engine doesn’t like the this keyword.”
but in that thread the “this” was a this.sourceRectAtTime, rather than what we have here: “thisLayer(…)” (and which works anyway).
I would have loved to have worked this out using the pointers you provided, and not bugged you and the forum for more assistance. Sadly I have struck a wall, and I’m not there yet with knowing how to troubleshoot this