Referencing a Polygon Object in a Multilayer Object
Essentially, you only need to add in your Polygon object ID to the Polygon expression in your Multilayer object.
Below are detailed steps to accomplish this.
Find the Properties for your Polygon Object
Right-click your Polygon Object, and click Properties.
Note the Object ID
Note the Object ID in the brackets after Properties. In this case, the Object ID is "CH42".
Add the Polygon Object ID to the Multilayer Object
Open the Properties of your Multilayer Object, and paste your Polygon Object ID in the expression box.
When the object reloads, you'll see your polygon(s) in the main map, and the polygon layer added to the layer control.
Note: The name of the layer in the layer control is the same as the caption of your Points object.
You can manage Points layer display with expressions, just like any other object.
NOTE: this particular Multilayer Object is using both Points and Polygon Objects. For information about configuring for the Polygon Object, read Referencing a Polygon Object in a Multilayer Object.