Object Spreads In Object Scope

In the scope of an object type, the only valid object type fragment spread is one that applies to the same type that is in scope.

For example

fragment dogFragment on Dog {
  ... on Dog {
    barkVolume
  }
}

and the following is invalid

fragment catInDogFragmentInvalid on Dog {
  ... on Cat {
    meowVolume
  }
}