Merge pull request #3958 from martinkupa/fix-docs

[Docs] Mention required order on form controls' modifiers

Author: jgthms

docs/documentation/form/general.html

@@ -915,7 +915,8 @@
     <li><code>icon is-left</code> if <code>has-icons-left</code> is used</li>
     <li><code>icon is-right</code> if <code>has-icons-right</code> is used</li>
   </ul>
-  <p>The size of the <strong>input</strong> will define the size of the icon container.</p>
+  <p>Make sure the input is the control's first child, otherwise the icon may disappear when selected. The size of the
+    <strong>input</strong> will define the size of the icon container.</p>
 </div>
 
 {% include docs/elements/snippet.html content=icons_example clipped=true %}