A SchemaComponent is an object in a schema.
While the schema is being built, a list of such objects is maintained,
and on completion, the fixup method is called to resolve forwards references.
Subsequently, the validate method is called to invoke validation
This method is called to look for cycles. The object implementing this
method is required (a) to raise an exception if the object itself appears
in the list of references, (b) to add itself to the list of references, and
(c) to call the lookForCycles method on all the objects that it references.
references - A stack of objects that contain direct or indirect references
to this object, and that must therefore not be referred to from this object.
Elaborate the schema component: after reloading a serialized schema component model,
this expands the component with derived information needed during validation episodes.
The model is assumed to be valid.