Debugging-What is green triangle in the margin?

I was debugging and my component froze (didn't respond to F8 or F5) and a green triangle appeared over the yellow arrow in the left-hand margin. Does anyone know what this is?

The green triangle is a stack pointer. When debugging you can call the program stack (CTRL-L) and see where other calls to subs/functions etc. were made. That way you can follow the run of your app.

<font color=green>Do or do not
There is no try</font color=green>

Thanks, much!