The handle
Every TQTXWidget instance is associated with a single DOM element (like a <DIV>, <BUTTON>, or <IMG>). This reference is stored in its Handle property. When you change a widget's property, you are simply using a pascal-friendly abstraction. Behind the scenes, the widget is translating accessing the element directly via it's Handle.
So when you write:
MyWidget.Left := 10;
This becomes a call to TQTXWidget.SetLeft() who in turn does this:
MyWidget.Handle.style.left = "10px";