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Whenever an ajax post is made, a full page with html 4 doctype is returned but I want to display that page on the current one."
If you wish to display one HTML page within another, I suggest you use an <iframe> element.
HTML iframe tag[
^]
"Dumping" one HTML page inside of another is bound to cause problems as improperly placed tags abound (two bodies, two headers, two HTML declarations and another DOCTYPE) - all of these out-of-place.