IFRAME interior functionality

I've been making a page with PHP and XML for awhile now and I've
actually finished it, but I recently got the urge to add a new feature
in case the queries from XML become too long (user defined with a
cookie, this feature will not even appear unless they define the cookie,
which I've already worked out).  The problem comes into play when I try
to enable the feature.   The feature is instead of just putting all of
the info into a new row/column, I want to put the entire table into an
IFRAME, and then limit the amount shown (of course it is scrollable) to
a user defined size (with a minimum of 10, but that doesn't matter).
 
I think that an IFRAME should be able to use inside information.  For
instance
 
<IFRAME SRC="add.php">  </IFRAME> works perfectly, assuming
I want to show add.php and that I'm not worried about the other
attributes.  However, if I want to use the IFRAME to, say, show
something from within itself (i.e., <IFRAME> Here is some text I
want to show up inside the IFRAME </IFRAME> should show "Here is
some text I want to show up inside the IFRAME" within an IFRAME).
However, unless the user's browser does not support frames, it doesn't
show anything from in between the IFRAME tags.
 
So, assuming that I can, I think IFRAME's should be able to leave out
the SRC attribute if they want to directly put information inside the
IFRAME.
 
I've thought about creating a script that makes an HTML file at midnight
comprised of information I need, but since the DB/XML information can be
updated any time during the day by anyone, that would never be reliable.
 
Thanks for your time,
Chris Earle