`editor.doesElementContainSelection`

Looking at this code, it's not obvious to me that this function will behave properly for multiply-nested selections.

If you have a selection denoted by the `|` characters in this HTML, does it properly return true if called on the `toTest` element?

```
<ol id="toTest">
  <li>
    <ol>
      <li>F|o|o</li>
    </ol>
  </li>
</ol>
``` 

Maybe worth adding that test, even if it does work?