Need help understand this construct function

[admin]

function ConstructObject(obj,nest){

nest=(!nest) ? '':'document.'+nest+'.'

//what are these two lines of code doing???
this.el = document.getElementById( obj );
this.css = this.el.style;

this.scrollHeight = this.el.offsetHeight
this.clipHeight = this.el.offsetHeight

this.up = MoveAreaUp;
this.down = MoveAreaDown;
this.MoveArea = MoveArea;
this.x;
this.y;
this.obj = obj + "Object"
eval(this.obj + "=this")
return this;
}