A marker interface for lazy composites. A lazy composite is a
CompositeEntity that does not automatically populate itself
with contained entities and relations when it is instantiated.
It does populate itself with attributes and ports, but the
contained entities and relations are not created until they
are explicitly requested.
Note that a class that implements this interface cannot
have parameters whose values are expressions that refer to
contained entities or relations or attributes contained by
those. This is a rather esoteric use of expressions, so
this limitation may not be onerous.