Warn about the list being conceptual

webrtc.html

@@ -8973,6 +8973,15 @@ <h2>
                   dictionaries representing the most optimistic view of the codecs the user
                   agent supports for sending media of the given <var>kind</var> (video or audio).
                 </p>
+                <p class="note">
+                  This conceptual list contains every combination of parameters that
+                  the user agent is capable of processing. In practice, this would
+                  be implemented as a piece of code that parses the parameters and
+                  determines whether they are acceptable or not, but this is highly
+                  codec dependent, so for the purpose of specification, we work with
+                  a conceptual list containing all acceptable parameter combinations.
+                </p>
+
                 <p>
                   The <dfn>list of implemented header extensions for sending</dfn>, given
                   <var>kind</var>, is an [=implementation-defined=] list of
@@ -10387,6 +10396,14 @@ <h2>
                   the codecs the user agent supports for receiving media of the given
                   <var>kind</var> (video or audio).
                 </p>
+                <p class="note">
+                  This conceptual list contains every combination of parameters that
+                  the user agent is capable of processing. In practice, this would
+                  be implemented as a piece of code that parses the parameters and
+                  determines whether they are acceptable or not, but this is highly
+                  codec dependent, so for the purpose of specification, we work with
+                  a conceptual list containing all acceptable parameter combinations.
+                </p>
                 <p>
                   The <dfn>list of implemented header extensions for receiving</dfn>, given
                   <var>kind</var>, is an [=implementation-defined=] list of