OptionalsideSide to fix the port to. Optional: when omitted it defaults to the flow axis (e.g. EAST/WEST for a RIGHT/LEFT layout), so data-flow ports sit on the left/right of a container by default. A port used as an edge's sourcePort defaults to the flow-forward side, as a targetPort to the flow-backward side.
OptionalsizeSquare size in px (default 12; sized to carry a direction glyph when ports learn flow direction).
A boundary port on a container or plain node.