Merge pull request #692 from ndw/iss-686

Add note about doc.xml, clean up external docs

xproc/src/main/xml/specification.xml

@@ -754,7 +754,7 @@ content types, that they accept. Input documents must
               <glossterm>implementation-defined</glossterm>.</impl>
         </para>
         <para>Version 3.0 of XProc does not require implementations to guarantee that multiple
-          attempts to dereference the same URI always produce consistent results.</para>
+          attempts to dereference the same URI always produce the same results.</para>
         <note xml:id="note-unsatisfying">
           <para>On the one hand, this is a somewhat unsatisfying state of affairs because it leaves
             room for interoperability problems. On the other, it is not expected to cause such
@@ -1069,6 +1069,13 @@ the document provided dynamically on the <port>source</port> port,
 any attempt to refer to <code>$D</code> in the expression(s) that
 initialize <code>$A</code> and <code>$B</code> would be an error.</para>
 
+<note>
+<title>Note</title>
+<para>There is no guarantee that the document read from <uri>doc.xml</uri> during
+static anlaysis will be the same as the document read later during dynamic evaluation.
+See <xref linkend="external-docs"/> for further discussion.</para>
+</note>
+
 <para>The results of XProc extension functions may differ during static analysis,
 as described in the description of each function.</para>