In php class variable one equal second variable? : <p>This is my code:</p>

<pre><code>class Config {
static public $site = 'http://localhost/site/';
static public $style = $site . 'css/style.css';

// ...
}
</code></pre>

<p>This is not work for me. I get white screen.</p>

<pre><code>class Config {
    static public $site = 'http://localhost/site/';
    static public $style = 'http://localhost/site/css/style.css';

    // ...
    }
</code></pre>

<p>This is work. I get design and code. Work very well. My question is Why?</p>
