Buttons has two different methods that can be used to format the data exported differently from the data that is shown in the table: orthogonal options and formatting functions as shown in this example. They both achieve basically the same thing in different ways: namely modification of the output data.
Formatting functions for export buttons are specified by assigning a function to one (or more) of the format object of the exportOptions object. Three formatting functions can be used: header, footer and body. This is the primarily advantage of using formatting functions over orthogonal data - the header and footer can also be formatted using this method (of course orthogonal and this formatting function method can both be used.