function _fnDrawHead( oSettings, aoSource, bIncludeHidden )
	{
		var i, iLen, j, jLen, k, kLen, n, nLocalTr;
		var aoLocal = [];
		var aApplied = [];
		var iColumns = oSettings.aoColumns.length;
		var iRowspan, iColspan;
	
		if ( ! aoSource )
		{
			return;
		}
	
		if (  bIncludeHidden === undefined )
		{
			bIncludeHidden = false;
		}
	
		/* Make a copy of the master layout array, but without the visible columns in it */
		for ( i=0, iLen=aoSource.length ; i<iLen ; i++ )
		{
			aoLocal[i] = aoSource[i].slice();
			aoLocal[i].nTr = aoSource[i].nTr;
	
			/* Remove any columns which are currently hidden */
			for ( j=iColumns-1 ; j>=0 ; j-- )
			{
				if ( !oSettings.aoColumns[j].bVisible && !bIncludeHidden )
				{
					aoLocal[i].splice( j, 1 );
				}
			}
	
			/* Prep the applied array - it needs an element for each row */
			aApplied.push( [] );
		}
	
		for ( i=0, iLen=aoLocal.length ; i<iLen ; i++ )
		{
			nLocalTr = aoLocal[i].nTr;
	
			/* All cells are going to be replaced, so empty out the row */
			if ( nLocalTr )
			{
				while( (n = nLocalTr.firstChild) )
				{
					nLocalTr.removeChild( n );
				}
			}
	
			for ( j=0, jLen=aoLocal[i].length ; j<jLen ; j++ )
			{
				iRowspan = 1;
				iColspan = 1;
	
				/* Check to see if there is already a cell (row/colspan) covering our target
				 * insert point. If there is, then there is nothing to do.
				 */
				if ( aApplied[i][j] === undefined )
				{
					nLocalTr.appendChild( aoLocal[i][j].cell );
					aApplied[i][j] = 1;
	
					/* Expand the cell to cover as many rows as needed */
					while ( aoLocal[i+iRowspan] !== undefined &&
					        aoLocal[i][j].cell == aoLocal[i+iRowspan][j].cell )
					{
						aApplied[i+iRowspan][j] = 1;
						iRowspan++;
					}
	
					/* Expand the cell to cover as many columns as needed */
					while ( aoLocal[i][j+iColspan] !== undefined &&
					        aoLocal[i][j].cell == aoLocal[i][j+iColspan].cell )
					{
						/* Must update the applied array over the rows for the columns */
						for ( k=0 ; k<iRowspan ; k++ )
						{
							aApplied[i+k][j+iColspan] = 1;
						}
						iColspan++;
					}
	
					/* Do the actual expansion in the DOM */
					$(aoLocal[i][j].cell)
						.attr('rowspan', iRowspan)
						.attr('colspan', iColspan);
				}
			}
		}
	}
Draw the header (or footer) element based on the column visibility states. The
methodology here is to use the layout array from _fnDetectHeader, modified for
the instantaneous column visibility, to construct the new layout. The grid is
traversed over cell at a time in a rows x columns grid fashion, although each
cell insert can cover multiple elements in the grid - which is tracks using the
aApplied array. Cell inserts in the grid will only occur where there isn't
already a cell in that position.
 @param {object} oSettings dataTables settings object
 @param array {objects} aoSource Layout array from _fnDetectHeader
 @param {boolean} [bIncludeHidden=false] If true then include the hidden columns in the calc,
 @memberof DataTable#oApi