Thank you for that posts, they also helped me a lot :)
Although I have one problem left. I used your second suggestion of
highlighting the components. My problem is:
When clicking on components and dragging them, the highlighted rectangle
stays in its former place after dropping the component on a different
place of the diagram. I would need that rectangle to move with the dragged
component. Or only allow highlighting on mouse click leave, so dragging
would not even be enabled for highlighting.
Any suggestions on how to do this? Thank you in advance!