Can I restrict what blocks that can be dropped into a container

My intent is to create a block that should allow only image components (I'm using the default one from grapes-blocks-basic) to be dropped inside it. I have the following test code: However, when I run the above code, what happens is that I can't drop an image component inside the Image Container. The green drop cursor only appears around the top/bottom/sides of the container but it won't appear inside it. Actually, I can't drop ANY component inside it. I kind of assumed that the "droppable" property could work the same way as the "draggable" property does in the example here: https://github.c...