When showing off some pictures of my Victor portable, I was asked what those black metal bits were at the back. These were the tab stops.
That triggered an immediate 'wow' that the tabs stops as are drawn on a ruler bar on a computer screen can be linked back to the typewriter.
The same way that the classic typewriter still is an 'icon' for 'writing', tab stops on a ruler bar have become the 'icon' for the tab function.
For many users of a graphical text editor (or 'word processor') the iconography of the ruler with margin stops and the tab stops is clear and evident. Even without being aware of the mechanical origins of the margins and tab setting functions, these are the recognized symbols that still make sense for aligning characters.