Several people have emailed me asking how I got this working in Plone, since the <iframe> tag is disallowed as "unsafe" HTML by Plone. And rightly so; if you allow untrusted users to add content to your Plone-based site, they can simply put in an <iframe> tag, and place their entire SPAM site right into a page in your site!!!

However, if you *do* trust all the users that add content to your site, then you can allow the <iframe ... > tag. Go to the Zope Management Interface for your site (log in, and go the the "site setup" link, and go to the "Zope Management Interface" link.

Then, select the "portal_transforms" link, and then the "safe_html" link. Then, go to the bottom, and add a new entry to the bottom of the "valid_tags" table: "iframe" and "1". Hit Submit, and you should be good to go! Now, the Plone engine won't strip the <iframe ...> tag from the HTML in your pages.