I'm really speaking about Notepad++: it has multiple "tabs", but only two can be visible (side by side: an editor 1 on the left, and an editor2 on the right).
The "tabs" are just buttons to select which text will go into one of the two possible editors (these two views may show different position in the same single document).
There's still no way to have 3 or 4 tabs simultaneously, either side by side, or below each other (which should be the prefered presentation for "tabs" open on the same document).