an object (entity) from a selection set
The name of the selection
set; otherwise nil, if the specified
entity is not in the set.
Note that the entity
is actually deleted from the existing selection set, as opposed
to a new set being returned with the element deleted.
In the following examples,
entity name e1 is a member
of selection set ss, while entity
name e3 is not a member
Selection set ss is returned with entity e1 removed.
The function returns nil because e3 is
not a member of selection set ss.