It looks like the Iframes now work, but a Video tag with Source tags does not, like the following:
<video class='embed-responsive embed-responsive h-100' controls='controls'>
<source src= '/File/101' type='video/webm' />
<source src='/File/108' type='video/mp4' />
The View HTML Button will remove the whole video tag. And the 'insertHtml' will throw an Error on the JS Console.
These Tags are necessary because different browsers and OSs may not be able to display certain media types. So usually you provide multiple sources for the different requirements. Is there a way to allow these Tags in the 'insertHtml' Method?