When you design a level, you can test it... but as soon as you press EDIT your test-level is lost.
It would be nice to have a test-level all the way trough the design phase. So you could fine tune a level withouth having to rebuild your solution for every time.
And IF that level could be saved, as a normal solution, that would help alot, especially on tricky contraptions that might take forever to build and time for perfection.
//Robert
