code: function ( cell, read, last, i, x, y ) {
  			// Increment a number if it is found
  			var re = /(\-?\d+)/;
  			var match = this.increment && last ? last.match(re) : null;
  			if ( match ) {
  				return last.replace( re, parseInt(match[1],10) + (x<0 || y<0 ? -1 : 1) );
  			}
  			return last === undefined ?
  				read :
  				last;
  		}
docs: Step function. This provides the ability to customise how the values
  are incremented.
  
  @param  {node} cell `th` / `td` element that is being operated upon
  @param  {string} read Cell value from `read` function
  @param  {string} last Value of the previous cell
  @param  {integer} i Loop counter
  @param  {integer} x Cell x-position in the current auto-fill. The
  starting cell is coordinate 0 regardless of its physical position
  in the DataTable.
  @param  {integer} y Cell y-position in the current auto-fill. The
  starting cell is coordinate 0 regardless of its physical position
  in the DataTable.
  @return {string} Value to write