<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>

You could look check
```
is_array()
```
on the first element, under the assumption that if the first element of an array is an array, then the rest of them are too.