How does PHP process functions in a file?
<p>Say I have <code>file.php</code> with three functions and an <code>echo</code> statement:</p>

<pre><code>function one() {
    return three() . ' This is one.';
}

function two() {
    return 'This is two.';
}

function three() {
    return 'This is three.';
}

echo one(); // string(xx) "This is three. This is one."
</code></pre>

<p>First, is it generally acceptable to have <code>function one()</code> call <code>function three()</code> even though <code>function three()</code> appears later in the file?</p>

<p>Second, when <code>file.php</code> is loaded in the browser (thus executing the PHP on the server), does PHP calculate the return value of <code>function two()</code>, even though it is never called?</p>

<p>Any links for further reading on how PHP process mundane things like this would be great.</p>
