title: NSRegularExpression
body: <p>I have a string like:</p>
  
  <pre><code>
  ?key=123%252Bf-34Fa&name=John
  ?name=Johon&key=123%252Bf-34Fa
  </code></pre>
  
  <p>I want to get the value for the <code>key</code>,I use this NSRegularExpression
  <code>
  (?i)(?&lt;=key=)[.?!&amp;]+[?=&amp;]??
  </code>
  What I think is that the pattern is like matching any character except "&amp;".But the result is always <code>NULL</code>.</p>
  
  <p>the value of each key can have anything except "&amp;".
  So How can I create the correct NSRegularExpression?
  thanks.</p>