Translation of the rules posted by Sirius @ https://forum.guildofwriters.org/viewtopic.php?p=73757#p73757
PotS is in worldspace when the mass is non-zero. Plasma likely detects
nonzero mass as "this object can move" and expects localspace. MOUL on
the other hand uses localspace if the object has a CI, otherwise
worldspace.
This allows for objects to print decals at runtime, like the baskets in
Eder Gira. Also, the same functionality can be hijacked for coincident
objects to exist as decals. This is basically a shortcut for adding hack
Z-flags to the base layer of a decal material.
I have also added some poll helpers to the idprops module so every time
we use an ID Datablock Property, we won't have to reinvent the wheel. I
also noticed that PointerProperties have to be a direct descendent of
`bpy.types.ID` otherwise Blender crashes. This kind of makes sense and
is not a huge issue to have to work around.