assertNotNull( possibleValuesService );
final Set<String> values = possibleValuesService.values();
assertNotNull( values );
final ContentProposalService contentProposalService = element.property( TestElement.PROP_SHAPES ).service( ContentProposalService.class );
assertNotNull( contentProposalService );
final ContentProposalService.Session session = contentProposalService.session();
assertNotNull( session );
Collection<ContentProposal> proposals;
proposals = session.proposals();