title: Layout format option to use for a width or height constraint?
body: <p>I'm using the visual format language to create width and height constraints in code. Like this:</p>
  
  <pre><code>[myView addConstraints:[NSLayoutConstraint
                          constraintsWithVisualFormat:@"V:[myView(100)]"
                                              options:NSLayoutFormatAlignmentMask
                                              metrics:nil
                                                views:views]];
  </code></pre>
  
  <p>But I really don't know what <code>NSLayoutFormatOption</code> I should be using for the options. One is required for the code to work, but <code>NSLayoutAttributeLeft</code> and the similar ones have nothing to do with width. What should I use for the option in this case?</p>