CKEditor.

The error came from some script in Application.js

public/javascripts/ckeditor/plugins/placeholder/dialogs/placeholder.js

@@ -0,0 +1,6 @@
+/*
+Copyright (c) 2003-2011, CKSource - Frederico Knabben. All rights reserved.
+For licensing, see LICENSE.html or http://ckeditor.com/license
+*/
+
+(function(){function a(b,c){var d=b.lang.placeholder,e=b.lang.common.generalTab;return{title:d.title,minWidth:300,minHeight:80,contents:[{id:'info',label:e,title:e,elements:[{id:'text',type:'text',style:'width: 100%;',label:d.text,'default':'',required:true,validate:CKEDITOR.dialog.validate.notEmpty(d.textMissing),setup:function(f){if(c)this.setValue(f.getText().slice(2,-2));},commit:function(f){var g='[['+this.getValue()+']]';CKEDITOR.plugins.placeholder.createPlaceholder(b,f,g);}}]}],onShow:function(){if(c)this._element=CKEDITOR.plugins.placeholder.getSelectedPlaceHoder(b);this.setupContent(this._element);},onOk:function(){this.commitContent(this._element);delete this._element;}};};CKEDITOR.dialog.add('createplaceholder',function(b){return a(b);});CKEDITOR.dialog.add('editplaceholder',function(b){return a(b,1);});})();