Frames - HTML and XHTML: The Definitive Guide - page 719

<iframe>

Function Defines an inline frame within a text flow

align , class , frameborder , height , id , long-
desc , marginheight , marginwidth , name ,
scrolling , src , style , title , width

Attributes

</iframe> ; never omitted End tag

Contains body_content

Used in text

Use the src attribute with <iframe> to specify the URL of the document
that occupies the inline frame. All of the other, optional attributes for
the <iframe> tag, including name , class , frameborder , id , longdesc , mar-
ginheight , marginwidth , name , scrolling , style , and title , behave exactly
like the corresponding attributes for the <frame> tag. [ The <frame> Tag,
11.4.1 ]

Use the content of the <iframe> tag to provide information to users of
browsers that do not support inline frames. Compliant browsers ignore
these contents, whereas all other browsers ignore the <iframe> tag and
therefore display its contents as though they were regular body content.
For instance, use the <iframe> content to explain to users what they are
missing: