To use pop-up menus in the instruction view, select text or position
  your mouse pointer in the instruction window, and press MB3.  The
  debugger inserts the selected text or line number in the menu items of
  the pop-up menu.

  If you press MB3 while your mouse pointer rests on an instruction
  source line in the instruction window, a pop-up menu with the following
  items appears:

  Examine [selection]    Evaluates the selected text and prints
                         its value in the command view.

  Toggle Breakpoint      Toggle breakpoint at your mouse pointer location.
    [line number]

  Display Source         Display source associated with instruction.

  Step-Instructions      Step to next instruction, stepping over routine
                         calls.

  Step                   Step to next line, stepping over routine calls.

  Go                     Resume execution of program.

  If you press MB3 while your mouse pointer rests in the annotation area
  of the instruction window, a pop-up menu with the following items
  appears:

  Toggle Breakpoint      Toggle breakpoint at your mouse pointer location.

  Step                   Step to next line, stepping over routine calls.

  Go                     Resume execution of program.