We want to use Video in Email. To do this you need to use HTML 5 and tag <video>.
Unfortunately, Marketo editor change <! Doctype html> to <! DOCTYPE HTML PUBLIC "- / / W3C / / DTD HTML 4.01 ...> and because of that <video> tag does not work.
It would be great if DOCTYPE was not changed. In this case we could use video playback in the ecards (in e-mail clients that support this functionality).