I think adding an eraser button when building planes would be pretty handy. Sometimes I put two blocks or pieces together and when I want to only drag one around it drags both. I understand that there's an undo button and I believe it shouldn't be replaced. I'm just suggesting to add an eraser button because I think that it would be quicker in some situations than undoing something. As I've stated before the undo button should still be kept even if the eraser button is added in, as the undo button has more capabilities and not every undo is to erase or necessarily remove something from the user's creation(i.e. when painting a plane part the wrong color, you'd undo that not erase because the part would be gone along with the color).