<p>
  To create a subsystem on a canvas, right-click on the canvas and select
  "create subsystem" from the context menu.
</p>
<p>
  All selected blocks will be placed in the subsystem and all connections 
  will be updated accordingly.
</p>
<p>
  To edit a subsystem canvas, double-click on the subsystem block to open the 
  corresponding canvas.
</p>
<p>
  To add new inputs or outputs to a subsystem do one of:
</p>
<il>
  <li> right-click on the subsystem canvas and select "Additional Blocks -> Input (or Output)"</li>
  <li> right-click on the subsystem block and select "Add Input" or "Add Output"; the corresponding terminals
  are placed on the subsystem canvas.</li>
</il>