Why are touchstart, touchmove, touchend values ​​shown relative to the viewport and not relative to the selected element?

Question

JavaScript

var el = document.createElement("div");
el.addEventListener('touchmove', function(event){
  if(event.targetTouches.length==1){
    var touch = event.targetTouches[0];
    console.log(touch.pageX+"px,"+touch.pageY+"px");
  }
}, false);
el.textContent = " ";
el.style.height = 400+"px";
el.style.border = "1px solid red";
el.style.margin = 100+"px";
document.body.appendChild(el);

Answer 1

And what's the problem, you take the first value as 0, and you calculate from it. True, the touchmove will be updated even if you go beyond the element. But you can decide by touch