function _block_header($xbeg, $xlen, $ybeg, $ylen) { if ($xlen > 1) { $xbeg .= "," . ($xbeg + $xlen - 1); } if ($ylen > 1) { $ybeg .= "," . ($ybeg + $ylen - 1); } return $xbeg . ($xlen ? $ylen ? 'c' : 'd' : 'a') . $ybeg; }