Subgroup (group in group) in favourites.xml

It seems not possible to make groupes like this:

<group name="Group">
    <item name="POI A" lat="12345" lon="56789"/>
    <item name="POI B" lat="12345" lon="56789"/>
    <group name="Subgroup">
        <item name="POI C" lat="12345" lon="56789"/>
        <item name="POI D" lat="12345" lon="56789"/>
    </group>
</group>


;(
Why?