title: Adding priority to layout constraints
body: <p>I have a <code>label</code> and <code>button</code> in a <code>superView</code> like this.</p>
  
  <pre><code>|--------------[Label]-----[button]-|
  </code></pre>
  
  <p>I'd like the <code>label</code> to be <code>centred</code> if possible, then have a min gap to the <code>button</code> and move to the left.</p>
  
  <p>So if the button is big it looks like...</p>
  
  <pre><code>|-[        LABEL!        ]-[button]-|
  </code></pre>
  
  <p>So, the button stays where it is and at the same size. And there are minimum gaps between the elements.</p>
  
  <p>I can add the <code>centerX</code> constraint but I can't seem to give it a priority so it remains <code>Required</code>.</p>
  
  <p>How can I create this situation? I'm doing all the auto layout in code.</p>
  
  <p>The constraints I currently have are...</p>
  
  <pre><code>[self addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"|-[_label]-(&gt;=8@1000)-[_button(==45)]-|"
                                                               options:NSLayoutFormatAlignAllCenterY
                                                               metrics:nil
                                                                 views:views]];
  
  [self addConstraint:[NSLayoutConstraint constraintWithItem:_label
                                                   attribute:NSLayoutAttributeCenterX
                                                   relatedBy:NSLayoutRelationEqual
                                                      toItem:self.contentView
                                                   attribute:NSLayoutAttributeCenterX
                                                  multiplier:1.0
                                                    constant:0.0]];
  </code></pre>
  
  <p>But I'm not sure how to reduce the priority of the second constraint.</p>