The HTML validator checks the HTML of your post to see that it is valid.
It also rejects numerous tags, such as <object> for security reasons.
This may be a problem for including YouTube videos, but there is a plugin for doing this without any security issues.
To disable the checker, edit the User Group Settings of the concerned user group; navigate to Users > User Groups > Actions.
Choosing ‘Basic security checking’ will disable the strongly enforced security filters.
Created by • Last edit by on Oct 20, 2015