site.com/core/admin/quota
check "allow ALL HTML tags"
Quote: If this options is checked, then ALL HTML tags will be allowed for profiles in this quota.
WARNING! Enabling this option will allow users to embed HTML tags that could compromise your system security or affect the design and/or layout of your pages.
Enabling this option overrides the "Allowed HTML Tags" option below.
Default: off
Yes there is a discussion about embedding iFrames and scripts being blocked. the end result was "Yes its a security risk, yes its difficult for a purpose, but its being asked for so much, we give up, here you go."
You can search for those threads in this forum if your interested.