editorial: define and link _OneOf Input Object_

Author: leebyron

spec/Section 3 -- Type System.md

@@ -1570,10 +1570,10 @@ objects have a separate type in the system.
 
 **OneOf Input Objects**
 
-OneOf Input Objects are a special variant of Input Objects where the type system
-asserts that exactly one of the fields must be set and non-null, all others
-being omitted. This is useful for representing situations where an input may be
-one of many different options.
+:: A _OneOf Input Object_ is a special variant of Input Object where the type
+system asserts that exactly one of the fields must be set and non-null, all
+others being omitted. This is useful for representing situations where an input
+may be one of many different options.
 
 When using the type system definition language, the `@oneOf` directive is used
 to indicate that an Input Object is a OneOf Input Object (and thus requires
@@ -1683,7 +1683,7 @@ is constructed with the following rules:
   variable definition does not provide a default value, the input object field
   definition's default value should be used.
 
-Further, if the input object is a OneOf Input Object, the following additional
+Further, if the input object is a _OneOf Input Object_, the following additional
 rules apply:
 
 - If the input object literal or unordered map does not contain exactly one
@@ -1779,7 +1779,7 @@ input ExampleOneOfInputObject @oneOf {
       returns {true}.
    4. If input field type is Non-Null and a default value is not defined:
       1. The `@deprecated` directive must not be applied to this input field.
-   5. If the Input Object is a OneOf Input Object then:
+   5. If the Input Object is a _OneOf Input Object_ then:
       1. The type of the input field must be nullable.
       2. The input field must not have a default value.
 3. If an Input Object references itself either directly or through referenced
@@ -1811,7 +1811,7 @@ defined.
    Input Object type.
 5. The `@oneOf` directive must not be provided by an Input Object type
    extension.
-6. If the original Input Object is a OneOf Input Object then:
+6. If the original Input Object is a _OneOf Input Object_ then:
    1. All fields of the Input Object type extension must be nullable.
    2. All fields of the Input Object type extension must not have default
       values.

spec/Section 4 -- Introspection.md

@@ -151,7 +151,7 @@ type __Type {
   ofType: __Type
   # may be non-null for custom SCALAR, otherwise null.
   specifiedByURL: String
-  # should be non-null for INPUT_OBJECT only
+  # must be non-null for INPUT_OBJECT, otherwise null.
   isOneOf: Boolean
 }
 
@@ -375,8 +375,8 @@ Fields\:
 - `inputFields` must return the set of input fields as a list of `__InputValue`.
   - Accepts the argument `includeDeprecated` which defaults to {false}. If
     {true}, deprecated input fields are also returned.
-- `isOneOf` must return {true} when representing a OneOf Input Object, {false}
-  otherwise.
+- `isOneOf` must return {true} when representing a _OneOf Input Object_,
+  otherwise {false}.
 - All other fields must return {null}.
 
 **List**

spec/Section 5 -- Validation.md

@@ -43,7 +43,7 @@ type Query {
 
 type Mutation {
   addPet(pet: PetInput!): Pet
-  addPets(pet: [PetInput!]!): [Pet]
+  addPets(pets: [PetInput!]!): [Pet]
 }
 
 enum DogCommand {
@@ -1951,7 +1951,7 @@ IsNonNullPosition(locationType, variableUsage):
 - If the location of {variableUsage} is an {ObjectField}:
   - Let {parentObjectValue} be the {ObjectValue} containing {ObjectField}.
   - Let {parentLocationType} be the expected type of {ObjectValue}.
-  - If {parentLocationType} is a OneOf Input Object type, return {true}.
+  - If {parentLocationType} is a _OneOf Input Object_ type, return {true}.
 - Return {false}.
 
 AreTypesCompatible(variableType, locationType):