After this method is called (the call is made automatically)
the receiver will be attached to a `primitive' widget (which
can be in turn another extended widget).
This method is public not because you can call it, but because
it can be useful to override it, not forgetting the call to
super (which only calls #newPrimitive and saves the result),
to perform some initialization on the primitive widget
just created; overriding #create is in fact more generic than
overriding #newPrimitive. For an example of this, see the
implementation of BButtonLike.
newPrimitive
Create and answer a new widget on which the implementation of the
receiver will be based. You should not call this method directly;
instead you must override it in BExtended's subclasses.