How does cursor.track work

How does the cursor.track work please

In my code I make a selection like I did in the picture below

When I use code with cursor.rewind(2) (endOfSelection) I get cursor.track = 3 but when I do cursor.rewind(1) beggining of a selection I get cursor.track = 0

Can anyone explain me what is going on

import QtQuick 2.0
import MuseScore 3.0

MuseScore {
menuPath: "Plugins.pluginName"
description: "Description goes here"
version: "1.0"
onRun: {
var cursor = curScore.newCursor()
cursor.rewind(2)
console.log(cursor.track)
}
}