Basically, an error that pops up when one of the following blocks is called:
I think this would help in preventing people from trying to crash Snap! and others' browsers (even if you can close the tab, some young children might fry their computer's components running a Snap! crashing project (exaggeration)). It also helps in development. For example, sometimes I accidently do something like the image above and it takes a minute or two (on my ancient Windows 7, AMD Vision Premium) to stop the script. It's quite frustrating... Thank you devs!