NaCl documentation: add links for x86-{32,64} and MIPS32.

native_client_sdk/doc_generated/reference/sandbox_internals/index.html

 {{+bindTo:partials.standard_nacl_article}}
 
 <section id="sandbox-internals">
 <span id="sandbox-internals-index"></span><h1 id="sandbox-internals"><span id="sandbox-internals-index"></span>Sandbox Internals</h1>
 <p>The sandbox internals documentation describes implementation details for
 Native Client sandboxing, which is also used by Portable Native
 Client. These details can be useful to reimplement a sandbox, or to
 write assembly code that follows sandboxing rules for Native Client
 (Portable Native Client does not allow platform-specific assembly code).</p>
+<p>As an implementation detail, the Native Client sandboxes described here
+are currently used by Portable Native Client to execute code on the
+corresponding machines in a safe manner. The portable bitcode contained
+in a <strong>pexe</strong> is translated to a machine-specific <strong>nexe</strong> before
+execution. This may change at a point in time: Portable Native Client
+doesn&#8217;t necessarily need these sandboxes to execute code on these
+machines. Note that the Portable Native Client compiler itself is also
+untrusted: it too runs in a Native Client sandbox described below.</p>
 <p>Native Client has sandboxes for:</p>
 <ul class="small-gap">
 <li><a class="reference internal" href="/native-client/reference/sandbox_internals/arm-32-bit-sandbox.html#arm-32-bit-sandbox"><em>ARM 32-bit</em></a>.</li>
-<li>x86-32</li>
-<li>x86-64</li>
-<li>MIPS32</li>
+<li>x86-32: the original design is described in <a class="reference external" href="http://research.google.com/pubs/archive/34913.pdf">Native Client: A Sandbox
+for Portable, Untrusted x86 Native Code</a>, the current
+design has changed slightly since then.</li>
+<li>x86-64: the original design is described in <a class="reference external" href="http://research.google.com/pubs/archive/35649.pdf">Adapting Software Fault
+Isolation to Contemporary CPU Architectures</a>, the current
+design has changed slightly since then.</li>
+<li>MIPS32, described in the <a class="reference external" href="https://code.google.com/p/nativeclient/issues/attachmentText?id=2275&amp;aid=22750018000&amp;name=native-client-mips-0.4.txt">overview of Native Client for MIPS</a>,
+and <a class="reference external" href="https://code.google.com/p/nativeclient/issues/detail?id=2275">bug 2275</a>.</li>
 </ul>
 </section>
 
 {{/partials.standard_nacl_article}}