title: Checking if array is multidimensional or not?
body: <ol>
  <li>What is the most efficient way to check if an array is <strong>a flat array
  of primitive values</strong> or if it is a <strong>multidimensional array</strong>?</li>
  <li>Is there any way to do this without actually looping through an
  array and running <code>is_array()</code> on each of its elements?</li>
  </ol>