In WordPress when I add an autoplay function to videos, when I switch from text to visual code is added (mce_SELRES_start) and it messes everything up.
<span data-mce-type="bookmark" style="display: inline-block; width: 0px; overflow: hidden; line-height: 0;" class="mce_SELRES_start"></span>
eg.
<iframe src="[login to view URL]" width="560" height="315" frameborder="0" allowfullscreen="allowfullscreen"><span data-mce-type="bookmark" style="display: inline-block; width: 0px; overflow: hidden; line-height: 0;" class="mce_SELRES_start"></span></iframe>