In a tag value change script, I accidentally left the colon off the end of a while statement.
There was no visual indication of the error in the text of the script. (Later I saw that there is a thin red bar on the right side of the frame, six or eight lines down, where it becomes clear to the syntax checker that the colon is never going to be found.)
No error was reported when I clicked OK on the UDT definition dialogue.
At run time, the script did not execute in response to the trigger, presumably because compilation failed. I didn’t see any alarm on the Designer GUI. There is no report of the failure in the wrapper log.
Seems like a script that will not compile should be rejected at click of OK on the UDT definition dialog.