Add "vertex group" to collision

say for example you have cloth simulation colliding with one mesh but not another. It works great. but if you want collision with one PART of the mesh but not another, you can't. you need to make a fake duplicate proxy mesh. but in that case, that proxy mesh also has to move in the same way as the original mesh, which in some cases is not possible. one example is when using geonodes. all meshes are part of the same object, and simply making a duplicate without part of the mesh you don't want to collide has different results, in many different scenarios (indices, vertex count, randomness, sized based stuff, etc).

a great solution would be to just add vertex group to the collision modifiers, so you can define what parts of a mesh are a collider vs not, rather than having the whole mesh be a collider. this also allows it to be dynamic, e.g. controlled with geometry nodes.