Merge pull request #11224 from twbs/10506-doc

Document that uncollapsing the mobile navbar requires JS

components.html

@@ -2021,6 +2021,10 @@ <h2 id="navbar-default">Default navbar</h2>
       <h4>Customize the collapsing point</h4>
       <p>Depending on the content in your navbar, you might need to change the point at which your navbar switches between collapsed and horizontal mode. Customize the <code>@grid-float-breakpoint</code> variable or add your own media query.</p>
     </div>
+    <div class="bs-callout bs-callout-danger">
+      <h4>Requires JavaScript</h4>
+      <p>If JavaScript is disabled and the viewport is narrow enough that the navbar collapses, it will be impossible to expand the navbar and view the content within the <code>.navbar-collapse</code>.</p>
+    </div>
     <div class="bs-callout bs-callout-warning" id="multiple-navbars-warning">
       <h4>Multiple navbars require custom code</h4>
       <p>Multiple nearby navbars with dropdown menus are not supported by default. You will need to override the <code>z-index</code>es of the dropdown menus yourself. Otherwise, the dropdown menu will display behind the other navbar.</p>