Revise wording for normative definition

Author: Michael Wilson

index.html

@@ -170,9 +170,8 @@ <h2>
         <dfn>System Exclusive</dfn> are defined in [[MIDI]].
       </p>
       <div class="note">
-        The definition of a <dfn>valid MIDI message</dfn> should be
-        inferred from [[MIDI]], but the following may be used as a
-        non-normative guide:
+        <dfn>Valid MIDI message</dfn> is defined in [[MIDI]]. The
+        following may be used as a non-normative guide:
         <ul>
         <li>The first byte (the status byte) should have the high bit
         set, any following bytes should not unless they are part of a