code: public String getDuplicateNameErrorMessage(IEObjectDescription description, EClass clusterType, EStructuralFeature feature) {
  		EObject object = description.getEObjectOrProxy();
  		String shortName = String.valueOf(feature != null ? object.eGet(feature) : "<unnamed>");
  		StringBuilder result = new StringBuilder(64);
  		result.append("Duplicate ");
  		result.append(getTypeLabel(clusterType));
  		result.append(" '");
  		result.append(shortName);
  		result.append("'");
  		if (isContainerInformationHelpful(description, shortName)) {
  			EObject container = getContainerForErrorMessage(object);
  			if (container != null) {
  				String containerTypeLabel = getTypeLabel(container.eClass());
  				EStructuralFeature containerNameFeature = getNameFeature(container);
  				if (isContainerInformationHelpful(description, container, containerTypeLabel, containerNameFeature)) {
  					result.append(" in ");
  					result.append(containerTypeLabel);
  					if (containerNameFeature != null) {
  						String containerName = String.valueOf(container.eGet(containerNameFeature));
  						if (containerName != null) {
  							result.append(" '");
  							result.append(containerName);
  							result.append("'");
  						}
  					}
  				}
  			} 
  		}
  		return result.toString();
  	}
docs: Build the error message for duplicated names. The default implementation will provider error messages
  of this form:
  <ul>
  <li>Duplicate Entity 'Sample'</li>
  <li>Duplicate Property 'Sample' in Entity 'EntityName'</li>
  </ul>
  If the container information will be helpful to locate the error or to understand the error
  it will be used, otherwise only the simple format will be build. Clients may override different
  methods that influence the error message.
  @see #getNameFeature(EObject)
  @see #getTypeLabel(EClass)
  @see #getContainerForErrorMessage(EObject)
  @see #isContainerInformationHelpful(IEObjectDescription, String)
  @see #isContainerInformationHelpful(IEObjectDescription, EObject, String, EStructuralFeature)