Editorial: clarify potential execution environment

source

@@ -96911,7 +96911,11 @@ new PaymentRequest(…); // Allowed to use
   <h5>Environments</h5>
 
   <p>An <dfn export>environment</dfn> is an object that identifies the settings of a current or
-  potential execution environment. An <span>environment</span> has the following fields:</p>
+  potential execution environment (i.e., a <span data-x="navigation params">navigation
+  params</span>'s <span data-x="navigation-params-reserved-environment">reserved environment</span>
+  or a <span data-x="concept-request">request</span>'s <span
+  data-x="concept-request-reserved-client">reserved client</span>). An <span>environment</span> has
+  the following fields:</p>
 
   <dl>
    <dt>An <dfn data-x="concept-environment-id" export