property grew

This property returns true when the box has grown beyond it's calculated size in response to it's children requiring more space provided by the parent box.

var bx = scene.getBoxById("testBox");
var parBox = null;
if (bx) 
{
    bx.width = 256;
    bx.height = 159;

    parBox = bx.parent;
    if (parBox && parBox.grew)
    {
        // Now you could call a function to reposition your content
        UserRepositionContentFunc();
    }
}