Edit multiple lines at the same time

It seems there is already some sort of multi line selection possible with alt key.

That is selecting a certain section of the lines, as oppose to selecting complete lines between the starting position and the current position of the cursor while selecting.
This would mainly be useful for multi line commenting, where I do not wish to use /* */ commenting style, but // and perhaps uncomment on line in between.

For comparison, notepad++ has this feature as explained above.