When you’re editing a relational view, the Set View list includes a “Menu Window”.
I don’t think you would embed this view in a relational view. Instead, you would pop up an instance of this view, because the Menu Window view is a tear-off menu.

The only example usage I could find is in %XSI_HOME%\Application\toolbars\Main_Shelf.xsitb:

            <item type="scriptbutton" label="Polygons" userwidth="108" userheight="18" scriptengine="VBScript" tooltip="">
               <scripttext>&lt;![CDATA[Set oView = Desktop.ActiveLayout.CreateView( &quot;Menu Window&quot;, &quot;title is not used&quot; )
oView.Move 200, 160 
oView.SetAttributeValue &quot;TargetContent&quot;, &quot;ModelGetPrimitive&amp;Polygon Mesh&quot; ]]&gt;</scripttext>
            </item>

So the targetcontent looks like “ModelGetPrimitive>PolygonMesh”.
The target content is composed by concatenating the module (Model), toolbar section (Get), and menu (Primitive), then an > symbol, and the menu command with no spaces.
hat tip: Luceric

The Menu Window is defined by the view %XSI_HOME%\Application\views\UITkMenuHost.xsivw.

In Softimage, a Menu Window view looks like this: