When you are writing code and you change your nesting level, it shows marker line if line which changes nesting (class, def, for, when, if,…) is on screen, and if it is not on screen, it pops notification showing you where you are.
For example if you have class World(), and it has 20 methods, and you go to newline while writing last one and press Backspace cursor will go one tab back (i use tabs) and it will draw marker up to start of function/method you are writing, and if you press Backspace once more, it will show start of class World() and couple of first lines in it.
And nvm, i got used to that notification time, so i dont need to change it 
Ah i am once more amazed by your IDE
Awesome work!