Reword

Author: benjie

spec/Section 6 -- Execution.md

@@ -18,10 +18,11 @@ A GraphQL service generates a response from a request via execution.
 - {extensions} (optional): A map reserved for implementers to extend the
   protocol however they see fit.
 
-Note: Since {extensions} is reserved for implementers, the only requirement is
-that, if present, it is a map. There are no additional restrictions on its
-contents. It is recommended that implementers use prefixes in {extensions} keys
-to avoid conflicts with other implementers.
+Note: {extensions} exists to provide implementers with a reserved location to
+include additional information in requests without risking conflicts with future
+versions of this specification. If present, {extensions} must be a map, but
+there are no additional restrictions on its contents. To avoid conflicts, we
+recommended implementers use unique prefixes for keys within {extensions}.
 
 Given this information, the result of {ExecuteRequest(schema, document,
 operationName, variableValues, initialValue)} produces the response, to be