HTML and CSS Reference
HTML5 proposes two new attributes for the iframe element: seamless and sandbox .
The seamless attribute effectively renders the iframe as an inline include, which allows
the parent document's CSS to affect the contents of the iframe :
<iframe src="content.html" name="thisframe" width="200"
height="300" seamless"> [alternate content] </iframe>
Here is the same example using XHTML style syntax:
<iframe src="content.htm" name="thisframe" width="200"
height="300" seamless="seamless"> [alternate content] </iframe>
The sandbox attribute “sandboxes” the iframe, essentially preventing it from pulling in
content from any source other than the iframe itself. Used without attributes, sandbox has
the following effects on the iframe :
• New windows cannot be created from within the iframe .
• Plug-ins are prohibited; embed , object , and applet will not function in
a sandboxed iframe .
• Nested inline frames are prohibited.
• A completely sandboxed iframe is considered, in essence, a new subdomain on the
• A completely sandboxed inline frame cannot submit forms or run scripts.
These prohibitions can be “turned off” using a number of attributes:
• allow-same-origin allows the iframe to pull in content from elsewhere in the
• allow-forms permits the submission of forms in the sandboxed iframe.
• allow-scripts allows the sandboxed iframe to run scripts from the same domain.
These attributes can be used separately, or together as space-separated values. The order of
the attributes does not affect any functionality.
<iframe src="content.htm" sandbox="allow-same-origin
<iframe src="content.htm" sandbox="allow-forms">
HTML5 drops presentational iframe attributes such as frameborder , scrolling ,
marginwidth , and marginheight . The attributes name , height , width , and the all-
important src remain part of the specification. HTML5 also adds global attributes to all
HTML5 tags, including <iframe> . See Chapter 3 for an in-depth discussion of these
Under HTML5, the <iframe> tag can also be written XHTML style, with a closing slash:
<iframe src="content.htm" height="200" width="200"