title: PHP isset function
body: <p>I believe I am a bit confused with the <code>isset</code> function in PHP. I'm trying to use this function to determine is a field in a form is <code>null</code>... I was under the impressions that the <code>isset</code> function checks to see if a field has a value in it... but I believe the <code>isset</code> function only determines if the thing passed to it exists.</p>
  
  <p>For example.</p>
  
  <p>If I have a form input field with the name attribute set to "day". I would use <code>isset($_GET['day']);</code> to determine if the form input field is not <code>null</code>? Or does <code>isset</code> just check to see if the 'day' exists and doesn't check that value that it passes?</p>
  
  <p>Any help would be great!
  Thanks!</p>