private getLineFeedCnt(bufferIndex: number, start: BufferCursor, end: BufferCursor): number {
// we don't need to worry about start: abc\r|\n, or abc|\r, or abc|\n, or abc|\r\n doesn't change the fact that, there is one line break after start.
pieceTreeBase.ts
// now let's take care of end: abc\r|\n, if end is in between \r and \n, we need to add line feed count by 1
if (end.column === 0) {
return end.line - start.line;
}