notes on optional, multiple realizations

conneg-by-ap/index.html

@@ -290,9 +290,13 @@ <h3>Archival Resource Key (ark)</h3>
   <section id="abstractmodel">
     <h2>Abstract Model</h2>
     <p>
-      This section describes an abstract conceptual model for content negotiation by profile, independent of any
+      This section describes a conceptual, abstract, model for content negotiation by profile, independent of any
       realizations of it within specific environments.
     </p>
+    <p>
+      Realizations of this abstract model MUST implement its functions, but how they do this will be
+      environment-specific.
+    </p>
     <section id="abstractmodelcontext">
       <h3>Context</h3>
       <p>
@@ -447,7 +451,18 @@ <h4>get resource by profile</h4>
   <section id="realizations">
     <h2>Realizations</h2>
     <p>
-      This section describes <em>realization</em>s of the abstract model in multiple implementation domains.
+      This section describes <em>realizations</em> of the abstract model which are implementations of it in different
+      environments.
+    </p>
+    <p>
+      This document provides onw two <em>realizations</em> however it is expected that implementers of content
+      negotiation by profile may implement further realizations in other environments.
+    </p>
+    <p class="note" title="Realization requirements">
+      Implementers of Content Negotiation by Profile need not implement multiple realizations of the
+      <a href="#abstractmodel">Abstract Model</a>. They need only implement the realizations relevant to them - either
+      those defined in this document or new ones they define, however each realization MUST accord with the Abstract
+      Model.
     </p>
     <section id="http">
       <h3>Hypertext Transfer Protocol Headers</h3>