Thrown if an object model operation would lead to a hierarchy that is not allowed in the
given object model implementation.
If this exception is encountered by a builder when creating an OM node from an event received
by the parser and if the corresponding content can be ignored (i.e. is not semantically
relevant), the builder should ignore the exception and skip the event. An example is whitespace
appearing before or after the root element of a document. This would be represented as an
OMText node below the OMDocument. If the OM implementation doesn't allow text
nodes as children of a document (as for example in DOM), it should throw this exception so
that the builder can discard the event.