little correction to Jompis:

if (0 <= $mergeRowSrcStart && $mergeRowSrcStart >= $srcRowStart && $mergeRowSrcEnd <= $srcRowEnd) {

change to

if ($mergeColSrcStart >= $srcColumnStart && $mergeColSrcEnd <= $srcColumnEnd && $mergeRowSrcStart >= $srcRowStart && $mergeRowSrcEnd <= $srcRowEnd) {