Let’s take the “Calculator” filter as an example: after entering a result attribute name and a formula and pressing Apply - not only the formula is evaluated!
On top of that, the render view switches to showing the new result attribute as current attribute for the display.
This is very nice and userfriendly, and I would like to add this behaviour also to some of my own filters. However: so far I was not able to figure out where exactly this is happening! I have written filters, with and without custom property widgets, and I know that communication between filters (server) and views (client) is always a bit tricky, but neither in the filter class code nor in the custom property widget code I found any “suspicious activity”…
Best regards and many thanks for helpful hints! Cornelis