removes extend from type definitions in Source Schema and Field Selection`

Author: PascalSenn

spec/Appendix A -- Field Selection.md

@@ -52,14 +52,14 @@ considered valid. For non-scalar arguments, you must specify each field of the
 input type in {SelectedObjectValue}.
 
 ```graphql example
-extend type Query {
+type Query {
   findUserByName(user: UserInput! @is(field: "{ firstName: firstName }")): User
     @lookup
 }
 ```
 
 ```graphql counter-example
-extend type Query {
+type Query {
   findUserByName(user: UserInput! @is(field: "firstName")): User @lookup
 }
 ```
@@ -846,7 +846,7 @@ In contrast, the following is invalid because it uses a field "address" which is
 not defined on the expected type:
 
 ```graphql counter-example
-extend type Query {
+type Query {
   storeById(id: ID! @is(field: "address")): Store! @lookup
 }
 
@@ -875,7 +875,7 @@ would create ambiguity and potential conflicts.
 For example, the following is invalid:
 
 ```graphql counter-example
-extend type Query {
+type Query {
   storeById(id: ID! @is(field: "id id")): Store! @lookup
 }
 
@@ -919,7 +919,7 @@ input UserInput {
 Then, an invalid selection would be missing the required `id` field:
 
 ```graphql counter-example
-extend type Query {
+type Query {
   userById(user: UserInput! @is(field: "{ name: name }")): User! @lookup
 }
 ```
@@ -928,7 +928,7 @@ If the `UserInput` type requires the `name` field, but the `User` type has an
 optional `name` field, the following selection would be valid.
 
 ```graphql example
-extend type Query {
+type Query {
   findUser(input: UserInput! @is(field: "{ name: name }")): User! @lookup
 }
 
@@ -947,7 +947,7 @@ But if the `UserInput` type requires the `name` field but it's not defined in
 the `User` type, the selection would be invalid.
 
 ```graphql counter-example
-extend type Query {
+type Query {
   findUser(input: UserInput! @is(field: "{ id: id }")): User! @lookup
 }
 

spec/Section 2 -- Source Schema.md

@@ -360,23 +360,23 @@ Note: In this case the `@is` directive could also be omitted as the argument and
 field names match.
 
 ```graphql example
-extend type Query {
+type Query {
   personById(id: ID! @is(field: "id")): Person @lookup
 }
 ```
 
 The `@is` directive also allows referring to nested fields relative to `Person`.
 
 ```graphql example
-extend type Query {
+type Query {
   personByAddressId(id: ID! @is(field: "address.id")): Person
 }
 ```
 
 The `@is` directive is not limited to a single argument.
 
 ```graphql example
-extend type Query {
+type Query {
   personByAddressId(
     id: ID! @is(field: "address.id")
     kind: PersonKind @is(field: "kind")
@@ -388,7 +388,7 @@ The `@is` directive can also be used in combination with `@oneOf` to specify
 lookup fields that can resolve entities by different keys.
 
 ```graphql example
-extend type Query {
+type Query {
   person(
     by: PersonByInput
       @is(field: "{ id } | { addressId: address.id } | { name }")
@@ -781,7 +781,7 @@ type Review {
   author: User @provides(fields: "email")
 }
 
-extend type User {
+type User {
   id: ID!
   email: String! @external
 }
@@ -819,7 +819,7 @@ type Product @key(fields: "id") {
 }
 
 # The new "Payments" schema:
-extend type Product @key(fields: "id") {
+type Product @key(fields: "id") {
   id: ID! @external
   price: Float! @override(from: "Catalog")
   tax: Float!
@@ -837,14 +837,14 @@ type Product @key(fields: "id") {
 }
 
 # The new "Payments" schema:
-extend type Product @key(fields: "id") {
+type Product @key(fields: "id") {
   id: ID! @external
   price: Float! @override(from: "Catalog")
   tax: Float!
 }
 
 # The new "Pricing" schema:
-extend type Product @key(fields: "id") {
+type Product @key(fields: "id") {
   id: ID! @external
   price: Float! @override(from: "Payments")
   tax: Float!
@@ -862,7 +862,7 @@ type Product @key(fields: "id") {
 }
 
 # The new "Payments" schema:
-extend type Product @key(fields: "id") {
+type Product @key(fields: "id") {
   id: ID! @external
   price: Float! @override(from: "Catalog")
   tax: Float!