Define an inline frame with the <iframe> tag. The <iframe> tag is not used within a <frameset> tag. Instead, it appears anywhere in your document that an <img> tag might appear. The <iframe> tag defines a rectangular region within the document in which the browser displays a separate document, including scrollbars and borders.

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 class, frameborder, id, longdesc, marginheight, marginwidth, name, scrolling, style, and title, behave exactly like the corresponding attributes for the <frame> tag. Section 11.4.1, "The <frame> Tag"

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

...other document content
<iframe src="sidebar.html" width=75 height=200 align=right>
Your browser does not support inline frames.  To view this
<a href="sidebar.html">document</a> correctly, you'll need 
a copy of Internet Explorer or the latest Netscape Navigator.
</iframe>
...subsequent document content

In this example, we let the user know that they were accessing an unsupported feature and provided a link to the missing content.

Except for their location within conventional document content, inline frames are treated exactly like regular frames. You can load other documents into the inline frame using its name (see following section) and link to other documents from within the inline frame.