<p>
  Blocks of type "LTPDA Block" (MBlock), "Subsystem Block" (MSubsystem), "MATLAB Expression Block" (MATBlock), 
  "Terminal Block" (MTerminal) all have input ports or output ports, or both. 
</p>
<p>
  These ports are connected together with "pipes" (MPipe is the underlying java class). Output ports
  can have more than one pipe connected; input ports can have only one pipe at a time. The binding object
  between a port and pipe is a "node" (MNode is the underlying java class). Nodes are displayed as small
  black circles.  
</p>
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<img src="images/block_connections.png" alt="Block Connections" border="3">
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</p>
<p>
  To connect these blocks together, do one of the following:
</p>
  <il>
    <li> Click and drag from one port to another.</li>
    <li> Click and drag from one output node to an input port.</li>
    <li> Click and drag from one output port to a block. Connection is made to the first free input (if there is one).</li>
    <li> Click and drag from one output node to a block. Connection is made to the first free input (if there is one).</li>
    <li> Select a source block, then ctrl-left-click a destination block to join the two. There must be at least one free
      input on the destination block. On the source block, the next free output is used, or the first output if no free 
    outputs are available.</li>
  </il>