RailwayRouteOptimization/scripts/View/Zoom/WindowZoom/doc/WindowZoom_proc_en.html

<div>
  <ol>
    <li>Specify the first corner of the area you want to view. Press the left
    mouse button at that corner and keep it down.</li>
    <li>Drag the mouse to the second corner of the area.</li>
    <li>Let go of the mouse button at the second corner.</li>
  </ol>
  <p>Note: Alternatively you can specify the first and the second corner each
  with a single mouse click instead of dragging the mouse around with the mouse
  button pressed.</p>
</div>