title: Get a value from array_keys
body: <p>maybe a simple question but I can't figure it out.. 
  I try to put values from an array in a variable, but it doesn't seem to work.</p>
  
  <blockquote>
    <p>$array = array(0 => 100, "color" => "red");</p>
    
    <p>print_r(array_keys($array));</p>
  </blockquote>
  
  <p>Outputs: </p>
  
  <pre><code>Array
  (
      [0] =&gt; 0
      [1] =&gt; color
  )
  </code></pre>
  
  <p>Then why can't I say: </p>
  
  <blockquote>
    <p>print_r(array_keys($array[1]));</p>
  </blockquote>
  
  <p>So it will output: <code>color</code></p>
  
  <p>How do I put <code>color</code> in a variable? </p>
  
  <p><em>*</em> Update: I work in PHP 5.3, unfortunately</p>
  
  <blockquote>
    <p>print_r(array_keys($array)[1]);</p>
  </blockquote>
  
  <p>don't work.</p>