diff --git a/spec/Section 4 -- Introspection.md b/spec/Section 4 -- Introspection.md
index 3e9777148..a231442e4 100644
--- a/spec/Section 4 -- Introspection.md	
+++ b/spec/Section 4 -- Introspection.md	
@@ -89,14 +89,17 @@ warnings.
 
 ## Type Name Introspection
 
-GraphQL supports type name introspection at any point within a query by the
-meta-field `__typename: String!` when querying against any Object, Interface,
-or Union. It returns the name of the object type currently being queried.
+GraphQL supports type name introspection within any selection set in an
+operation, with the single exception of selections at the root of a subscription
+operation. Type name introspection is accomplished via the meta-field
+`__typename: String!` on any Object, Interface, or Union. It returns the name of
+the concrete Object type at that point during execution.
 
 This is most often used when querying against Interface or Union types to
-identify which actual type of the possible types has been returned.
+identify which actual Object type of the possible types has been returned.
 
-This field is implicit and does not appear in the fields list in any defined type.
+As a meta-field, `__typename` is implicit and does not appear in the fields list
+in any defined type.
 
 
 ## Schema Introspection
@@ -110,8 +113,8 @@ __schema: __Schema!
 __type(name: String!): __Type
 ```
 
-These fields are implicit and do not appear in the fields list in the root type
-of the query operation.
+Like all meta-fields, these are implicit and do not appear in the fields list in
+the root type of the query operation.
 
 The schema of the GraphQL schema introspection system: