This left column must appear first in the HTML code. Using CSS, it is floated to the left side of the "wrapper" block that encloses all three columns.
If you assign a background color or image to this column, you will also need to style the "wrapper" block so that the background is matched when this isn't the longest column on the page.
This right column actually comes second in the code. This is necessary for it to line up with the top of the other two columns when floated.
This center column actually appears last in the HTML code. This is a necessary evil of this particular method. Only the absolute positioning method discussed previously allows this column to come first.
To leave room for the side columns, this center column has left and right margins equal to their respective widths (plus additional spacing).