If you ever tried putting an iframe in the Rich Text Field, you probably got what I got:

Server Error in '/' Application.
Empty strings are not allowed.
Parameter name: name

To solve this you have at least two options:

  1. Wrap your iframe with the xsl:template definition. This way the iframe will appear as a web control in the rich text editor, but will render fine on the content delivery.
<xsl:template match="*" mode="main">

<iframe id="iframe" src="..."></iframe>
  1. Turn off HtmlEditor.SupportWebControls setting in web.config:
<setting name="HtmlEditor.SupportWebControls" value="false"/>

The second option makes more sense since you don’t need to alter the rich text content. If you don’t paste webcontrols to the rich text field, go for it.