title: Is there a 'willSet' & 'didSet' I can intercept for UIScrollview.contentOffset?
body: <p>I have a situation where I need to gracefully move a frame when the <code>contentOffset.y</code> is a negative value.</p>
  
  <p>The problem is I don't want to get the <code>contentOffset</code> call <strong>AFTER</strong> the content has already been dropped below 0.</p>
  
  <p>Is there a <code>willSet</code> call where I can intercept it before the <code>UIScrollView</code> offsets its content?</p>