If the namespace display is in tree format, dragging the slider
  on a scroll bar produces a  navigation window     .

       Show the display with the Navigation Window.

  The navigation window contains a reduced image of the cur-
  rently expanded part of the namespace.  The box within the
  navigation window indicates the portion of the namespace
  where the slider is positioned; releasing MB1 displays that
  portion of the namespace in the namespace display window
  and closes the navigation window.

  To make the navigation window a separate, permanent win-
  dow, click on the button at the bottom right corner of the
  namespace display window.  Click on the same button to close
  the navigation window.

  To move around in the namespace display, point anywhere
  in the navigation window and drag the mouse up, down, left,
  or right to move the box that is inside the navigation window.

  When you release MB1, the portion of the namespace that is
  inside the box appears in the namespace display.