Main Content
With this layout you have the option of locating either the "Main Content" or the "Left Sidebar" first in the html source order.
The #inner div is nested within the #innerwrap div which has left and
right margins set on it. Those margins create the space for the left and right columns which are
shifted into place with negative margins.
This #main div is floated right and the #left div is floated left.
They are both nested in the #inner div which is floated right to bring them first in
the html source order while allowing the #right floated div to rise up to the same
vertical plane. The #main div is floated right so the #left div can be
floated left. That allows us to shift the #left div directly into the left margin of
the #innerwrap div.
Float containment is done with a "clearfix" adaption using a pseudo :after block on the
#innerwrap div for modern browsers and "haslayout" for IE 6&7.