title: In php, why array_unshift() is named unshift?
body: <p>As we know, there are four functions that can be used to insert into and delete from an array:</p>
  
  <ol>
  <li>array_push()</li>
  <li>array_pop()</li>
  <li>array_unshift()</li>
  <li>array_shift()</li>
  </ol>
  
  <p>What's the meaning of <code>array_unshift()</code> and <code>array_shift()</code>, I mean why they are named like this?</p>