title: How to check if isset is not set?
body: <p>I am using this line of code to check if isset is not set.</p>
  
  <p>for example :</p>
  
  <pre><code>if(!isset($_REQUEST['search']))
  { }
  else if(!isset($_REQUEST['submit']))
  {}
  </code></pre>
  
  <p>I just want to know if !isset is a valid code. If not, what is the proper method? Thanks</p>