The value of entPhysicalIndex for the physical entity which
'contains' this physical entity. A value of zero indicates
this physical entity is not contained in any other physical
entity. Note that the set of 'containment' relationships
define a strict hierarchy; that is, recursion is not
allowed.
In the event that a physical entity is contained by more
than one physical entity (e.g., double-wide modules), this
object should identify the containing entity with the lowest
value of entPhysicalIndex.