Where an opening, or the door or window filling one, sits in its host.
Null when expressId is neither, when it has no live host, or when the
opening is not placed relative to its host (an absolutely placed opening
has no offset along the wall to edit).
Where an opening, or the door or window filling one, sits in its host. Null when
expressIdis neither, when it has no live host, or when the opening is not placed relative to its host (an absolutely placed opening has no offset along the wall to edit).