y default there is just one port, the whole node, which results in the effect of having the whole node act as the port,
  as you have seen in all of the previous examples.
</p>
<p>
  To declare that a particular element in a <a>Node</a> is a port, set the <a>GraphObject.portId</a> property to a string.
  Note that the port-or-link-related properties may apply to any element in the visual tree of the node,
  which is why they are properties of <a>GraphObject</a> rather than <a>Node</a>.
</p>
<p>
  Port-like 