Each component in the virtual lab is descended from LabItem which controls standard properties such as position in the lab, construction of input and output ports, and display.
Normally there are no user-configurable parameters. At the advanced user level (see the parameters section) you have access to the drawing used to display the component in the lab. This must be a LabItemDrawing and can be created with the corresponding editor.
Each component specifies how many fluid and analog ports it has. If the drawing has appropriate ports marked, these e are used. Otherwise the ports are given default positions from the top left. The drawing also sets the preferred scale of the component.