Technical development.
Historically the three columns and a header has been produced using <table> layouts. This at first seems simple
At first glance all that is necessary is 2 rows and 3 columns with the header spanning the 3 columns. Cell padding and spacing can produce the desired white space and background colours can be used as well.
However if more than one section is required within each column or coloured borders as in this site are required it is necessary to resort to multiple nested tables. Also browsers may “collapse” cells with no content. This means that resized single pixel transparent .gif images are inserted to ensure that the cells cannot collapse.
Some apparently simple three column and a header may have up to 7 layers of nested tables each with a role to play in positioning content controlling cell border colours etc. This makes changing the layout very difficult even for the person who created it. It also bloats file sizes and in older browsers takes an appreciable time to render once the file has been downloaded. This particular layout would require at least 5 layers of nested tables to produce.
