title: Xcode Interface Builder. How Do These Autosizing Mask Settings Differ?
body: <p>I am now quite comfortable using autosizing masks in IB but there are two autosizing setting that I am not clear how they are intended to differ:</p>
  
  <p>Setting 1<br>
  <a href="http://dl.dropbox.com/u/11270323/stackoverflow/autosize-mask-0.png">Autosizing with both upper and lower anchors http://dl.dropbox.com/u/11270323/stackoverflow/autosize-mask-0.png</a>  </p>
  
  <p>Setting 2<br>
  <a href="http://dl.dropbox.com/u/11270323/stackoverflow/autosize-mask-1.png">Autosizing with only uppper anchor http://dl.dropbox.com/u/11270323/stackoverflow/autosize-mask-1.png</a>  </p>
  
  <p>Some context. The UIView subclass that uses these settings is a child subview. Setting 1 is giving me the behavior I want - subview expands/contracts with its parent view - while setting 2 is slightly different in a non-obvious way.</p>
  
  <p>What is the intended layout difference between these two settings?</p>
  
  <p>Thanks,<br>
  Doug</p>