[placeholder addon] Allow a DOM node to be given as placeholder content

Issue #3487

addon/display/placeholder.js

@@ -37,7 +37,9 @@
     var elt = cm.state.placeholder = document.createElement("pre");
     elt.style.cssText = "height: 0; overflow: visible";
     elt.className = "CodeMirror-placeholder";
-    elt.appendChild(document.createTextNode(cm.getOption("placeholder")));
+    var placeHolder = cm.getOption("placeholder")
+    if (typeof placeHolder == "string") placeHolder = document.createTextNode(placeHolder)
+    elt.appendChild(placeHolder)
     cm.display.lineSpace.insertBefore(elt, cm.display.lineSpace.firstChild);
   }
 

doc/manual.html

@@ -2762,9 +2762,10 @@ editor.setOption("extraKeys", {
 
       <dt id="addon_placeholder"><a href="../addon/display/placeholder.js"><code>display/placeholder.js</code></a></dt>
       <dd>Adds a <code>placeholder</code> option that can be used to
-      make text appear in the editor when it is empty and not focused.
-      Also gives the editor a <code>CodeMirror-empty</code> CSS class
-      whenever it doesn't contain any text.
+      make content appear in the editor when it is empty and not
+      focused. It can hold either a string or a DOM node. Also gives
+      the editor a <code>CodeMirror-empty</code> CSS class whenever it
+      doesn't contain any text.
       See <a href="../demo/placeholder.html">the demo</a>.</dd>
 
       <dt id="addon_fullscreen"><a href="../addon/display/fullscreen.js"><code>display/fullscreen.js</code></a></dt>