Input unions: improve accuracy of objection (#645)

* Improve accuracy of statement

* Typo

Co-Authored-By: Ivan Maximov <[email protected]>

Author: 2 people

rfcs/InputUnion.md

@@ -179,7 +179,7 @@ The premise of this RFC - GraphQL should contain a polymorphic Input type.
 
 Any data structure that can be modeled with output type polymorphism should be able to be mirrored with Input polymorphism. Minimal transformation of outputs should be required to send a data structure back as inputs.
 
-* Objection: input types and output types are distinct. Output types support aliases and arguments whereas input types do not. Marking an output field as non-nullable is a non-breaking change, but marking an input field as non-nullable is a breaking change.
+* Objection: composite input types and composite output types are distinct. Fields on composite output types support aliases and arguments whereas fields on composite input types do not. Marking an output field as non-nullable is a non-breaking change, but marking an input field as non-nullable is a breaking change.
 
 ### C) Doesn't inhibit [schema evolution](https://graphql.github.io/graphql-spec/draft/#sec-Validation.Type-system-evolution)