Gets any Atom that is part of this Element.
When an Atom is provided during construction, this may be a
reference to an IndirectObject rather than a direct reference to an
If this is the case then the reference needs to be resolved
through to an Atom.
This property stores the resolved Atom - usually a DictAtom but occasionally other types for
some specific types of Element.
However this property will never be a RefAtom as all references
have been resolved.