xkb - difference between modifier_map and SetMods

In the xkb guide on archlinux: https://wiki.archlinux.org/index.php/X_keyboard_extension
we see this configuration to set up LWIN as an ISO_Level3_Shift

   xkb_symbols { 
       key <LWIN> { [ISO_Level3_Shift ] };
       modifier_map Mod5 { ISO_Level3_Shift };
   }
   xkb_compatibility {
       interpret ISO_Level3_Shift { action= SetMods(modifiers=Mod5); };
   }

Now I am a bit confused.

• ISO_Level3_Shift is a virtual modifier. So we need to map it to a real modifier somehow. But what is the difference between modifier_map Mod5 { ISO_Level3_Shift }; and interpret ISO_Level3_Shift { action= SetMods(modifiers=Mod5); };? Why do we need both?

• In the xkb file compat/level5 I see things like

    interpret ISO_Level5_Shift+Any {
    useModMapMods= level1;
    virtualModifier= LevelFive;
    action= SetMods(modifiers=LevelFive);
    };
  
    interpret ISO_Level5_Shift {
    action= SetMods(modifiers=LevelFive);
    };
  

  What does useModMapMods and virtualModifier mean here?