What Is That Blue Box?

Ever noticed this blue box before and don’t know what it is?

Well this box lets you know that its an element that has been trimmed or has a solid element operations applied to it. In the image below, the box indicates that the wall has been trimmed to a roof. The second image lets me know that this wall has had a solid element operated with the roof.

You can even cancel a trim or solid element operation by clicking on the X