When creating MvParts you may want to place some nodes to hold a place for your connectors. It is not a requirement, but can come in handy. Here's a quick reference on customizing the output of your nodes.
Node Point: type "po" at the command line
DdPType: displays a dialog box for selecting PsMode and PdSize
PDMODE choices and what they deliver: 0=dot, 1=invisible, 2=+, 3=x, 4='
32-36 is the same as 0-4 w/ a circle around them
64-68 is the same as 0-4 w/ a square around them
96-100 is the same as 0-4 w/ a square and then a circle around them.
PDSIZE choices and what they deliver: 0=5% of height of the ScreenSize system variable
-10=(Negative) 10% of the viewport size
10=(Positive) 10 pixels in size