Strange NSLayoutConstraint Behavior
<p>I have a UIScrollView that I add a UITextView to.  I have the following constraint that I am also adding to the view:</p>

<pre><code>NSLayoutConstraint *xConstraint = [NSLayoutConstraint constraintWithItem:textView2 attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:_scrollView attribute:NSLayoutAttributeLeading multiplier:1.0 constant:50];
</code></pre>

<p>This constraint works perfectly but changing it from leading to trailing like so, has no effect.  It still displays based on the leading. </p>

<pre><code>NSLayoutConstraint *xConstraint = [NSLayoutConstraint constraintWithItem:textView2 attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:_scrollView attribute:NSLayoutAttributeTrailing multiplier:1.0 constant:50];
</code></pre>

<p>I have no understanding why the UITextView's location doesn't change position when I change the constraint from leading to trailing.  I realize that I would also need to change 50 to -50 if it was constraining to the trailing edge, but it isn't.</p>