System.Xml.Xsl.XmlQueryTypeFactory.IntersectItemTypes C# (CSharp) Method

        private XmlQueryType IntersectItemTypes(XmlQueryType left, XmlQueryType right) {
            Debug.Assert(left.Count == 1 && left.IsSingleton, "left should be an item");
            Debug.Assert(right.Count == 1 && right.IsSingleton, "right should be an item");
            if (left.TypeCode == right.TypeCode && (left.NodeKinds & (XmlNodeKindFlags.Document | XmlNodeKindFlags.Element | XmlNodeKindFlags.Attribute)) != 0) {
                if (left.TypeCode == XmlTypeCode.Node) {
                    return left;
                }
                // Intersect name tests
                XmlQualifiedNameTest nameTest = left.NameTest.Intersect(right.NameTest);

                // Intersect types
                XmlSchemaType type = XmlSchemaType.IsDerivedFrom(left.SchemaType, right.SchemaType, /* exept:*/XmlSchemaDerivationMethod.Empty) ? left.SchemaType :
                    XmlSchemaType.IsDerivedFrom(right.SchemaType, left.SchemaType, /* exept:*/XmlSchemaDerivationMethod.Empty) ? right.SchemaType : null;
                bool isNillable = left.IsNillable && right.IsNillable;

                if ((object)nameTest == (object)left.NameTest && type == left.SchemaType && isNillable == left.IsNillable) {
                    // left is a subtype of right return left
                    return left;
                }
                else if ((object)nameTest == (object)right.NameTest && type == right.SchemaType && isNillable == right.IsNillable) {
                    // right is a subtype of left return right
                    return right;
                }
                else if (nameTest != null && type != null) {
                    // create a new type
                    return ItemType.Create(left.TypeCode, nameTest, type, isNillable);
                }
            }
            else if (left.IsSubtypeOf(right)) {
                // left is a subset of right, so left is in the intersection
                return left;
            }
            else if (right.IsSubtypeOf(left)) {
                // right is a subset of left, so right is in the intersection
                return right;
            }
            return None;
        }