Can't add <iframe> to a Content element

 I can't seem to add an <iframe> element with Tailor. It works using the regular Wordpress editor.

Example: 
```
<iframe width="1280" height="720" src="https://www.youtube.com/embed/tfMyLMuaXjI?rel=0&amp;controls=0&amp;showinfo=0" frameborder="0" allowfullscreen></iframe>
```