This method will attempt to locate and return a child box object that has a tag
matching on the one provided by the caller. If the box has multiple boxes that match
the tag the first one found in the DOM will be returned.
var bx = scene.getBoxById("container");
if (bx)
{
var btn = bx.getBoxByTag("button");
if (btn)
{
btn.label = "Found button!";
}
}