Recently, one of my customers filed a ticket because some iFrame he got from another company wouldn't display after putting it into the content editor.
I told her it won't work because the (third-party) editor prohibits JavaScript inside iFrame tags and their attributes for security reasons.
She said ok. She said she'd understood the problem. And then, she reopened the ticket four (4!!!) times for the exact same reason, once because she tried to use a fixed iFrame tag the other company sent to her... still containing JavaScript, of course.

But, yeah... She understood what the problem was. Is clear.