In X11's standard Athena (aka Xt), right click is just another useful action, unrelated by default to popup menus.
- In the text widget, a right click extends the current text selection to the point of the click.
- In the scrollbar, a right click scrolls back. It brings the top row of the window to the cursor's (vertical) location. Co the further down you're located, the more it scrolls; the slider's location is irrelevant to this action. Contrary to popular belief, this is far more convenient than other, flashier scrollbars -- see badly designed scrollbars.