title: Syntax of Functions in PHP manual
body: <p>I have hard time understanding the syntax of the following function (and others alike):</p>
  
  <pre><code>int fwrite ( resource $handle , string $string [, int $length ] )
  </code></pre>
  
  <p>what is the meaning of the brackets and comma that follows <code>[, int $length ]</code>. what it should indicate?</p>