code: protected boolean isPartOfExpressionTree(EObject container) {
  		if (container instanceof XExpression) {
  			return true;
  		}
  		EClass type = container.eClass();
  		return type == XbasePackage.Literals.XCASE_PART || type == XbasePackage.Literals.XCATCH_CLAUSE || type == XAnnotationsPackage.Literals.XANNOTATION_ELEMENT_VALUE_PAIR;
  	}
docs: Returns true if the container can be nested within the expression tree. First and foremost that's
  true if the container itself is an expression. Other possible types are {@link XCasePart},
  {@link XCatchClause} or {@link XAnnotationElementValuePair}. Clients may override.