Question

How would I insert a container div using jQuery?

From
<div id="page">
<!-- a bunch of html and content !-->
</div>

To
<div id="page">
<div id="new-container">
<!-- a bunch of html and content !-->
</div>
</div>

Answer 1

$('#page').contents().wrapAll('<div id="new-container">');

See http://jsfiddle.net/U6gpu/1/.
contents() is used to select the content of an element, and wrapAll() to wrap the contents in a fresh container.