[Mapcss] Subselectors

[Thomas Davie]

I'm just trying to get straight in my head exactly what the semantics of a subselector in MapCSS is depending on the combination of node/way/relation/area/line used.

1) Are ways ever contained within areas/lines i.e. does area[landuse=comercial] way[barrier=fence] have any meaning beyond area[landuse=comercial][barrier=fence].  My gut feeling is that "area" "line" and "way" all describe the same thing, but with subtle preconditions, and thus should not be usable in subselectors in this way.  Is this correct?

2) Given the above it becomes clear that relation becomes the parent, beneath which you may have a choice of area/line/way (or possibly none), beneath which the nodes that make up the areas lines and ways sit.  The implication of that to me is that
relation[type=multipolygon] node[barrier=bollard] should select all nodes tagged barrier=bollard that are a member of any way that is a member of a multipolygon relation.  Is this correct?

Thanks

Bob