Iframe without src but still has content?

Yes, Here is how you change the html of the iframe with jQuery

var context = $('iframe')[0].contentWindow.document,
    $body = $('body', context);
$body.html('Cool');

Demo: http://jsfiddle.net/yBmBa/

document.contentWindow: https://developer.mozilla.org/en-US/d...

Yes, it is possible to load an empty <iframe> (with no src specified) and later apply content to it using script.

See: http://api.jquery.com/jquery-wp-content/themes/jquery/js/main.js (line 54 and below).

Or simply try:

<iframe></iframe>

<script>
document.querySelector('iframe')
        .contentDocument.write("<h1>Injected from parent frame</h1>")
</script>

Looks like this is the most compatible solution across browsers and also it is recognized by the W3C

<iframe src="about:blank"></iframe>

Sure. You can get a reference to the iframe's document object with

var doc = iframe.contentDocument;

and then you can create and add elements like you do in the current document.

If the iframe doesn't have a src attribute, it will still contain an empty document. I believe though that at least older IE versions require the src attribute to be set, otherwise the iframe won't have a document.

See also: contentDocument for an iframe.