Update User Guide

incoming/controllers.html

@@ -329,7 +329,9 @@
 </div>
 <section id="what-is-a-controller">
 <h2><a class="toc-backref" href="#id1">What is a Controller?</a><a class="headerlink" href="#what-is-a-controller" title="Permalink to this headline"></a></h2>
-<p>A Controller is simply a class file that handles a HTTP request. <a class="reference internal" href="routing.html"><span class="doc">URI Routing</span></a> associates a URI with a controller.</p>
+<p>A Controller is simply a class file that handles a HTTP request.
+<a class="reference internal" href="routing.html"><span class="doc">URI Routing</span></a> associates a URI with a controller. It returns a
+view string or <code class="docutils literal notranslate"><span class="pre">Response</span></code> object.</p>
 <p>Every controller you create should extend <code class="docutils literal notranslate"><span class="pre">BaseController</span></code> class.
 This class provides several features that are available to all of your controllers.</p>
 </section>

installation/upgrade_controllers.html

@@ -313,6 +313,8 @@
 <li><p>CI4 provides <a class="reference internal" href="../incoming/incomingrequest.html"><span class="doc">Request</span></a> and <a class="reference internal" href="../outgoing/response.html"><span class="doc">Responses</span></a>
 objects for you to work with - more powerful than the CI3-way.</p></li>
 <li><p>If you want a base controller (<code class="docutils literal notranslate"><span class="pre">MY_Controller</span></code> in CI3), use <strong>app/Controllers/BaseController.php</strong>.</p></li>
+<li><p>Calling <code class="docutils literal notranslate"><span class="pre">echo</span></code> within Controllers, as in CI3, is still supported, but
+it is recommended that a string or Response object be returned from Controllers.</p></li>
 </ul>
 </section>
 <section id="upgrade-guide">