document.designMode controls whether the entire document is editable. Valid values are
off. According to the specification, this property is meant to default to
off. Firefox follows this standard as does Chrome from version 43 onward. Webkit and earlier versions of Chrome default to
<iframe>'s document editable:
iframe_node.contentDocument.designMode = "on";
The definition of 'designMode' in that specification.
|Editor's Draft||Initial definition.|