A modest proposal for a new property

[hh]

I asked because I thought QL's proposal might be based on a new algorithm?

There are already (partial) solutions to that:

In LCS getting "transparency" clicks of cross-layered objects is hard but
possible for a big class of regions (see stack #47 = "pointInShape" of
the Raspi stacks collection, July 2015).

For LCB I already implemented "transparency clicks" for rotated rectangular
shapes in my last two (already shared) widgets. Just now also for a bit more
complicated shapes (-> LC Global, Nov).

Both methods are based on the subdivison algorithm by MShimrat (Aug 1962).
This algorithm is in LCB/LC 9.0.0-dp9 *very* fast, by the way, usable in a
mouseDown handler for checking regions defined by several hundred points.

For more general regions (closed polygons), as Quentin L. suggests, this
algorithm is also applicable, *without change* as long as the region-polygons
are not self-intersecting.