title: Operator Precedence and associativity
body: <p>I don't inderstand why this instruction will output 5. And how PHP interpreter will execute it.</p>
  
  <pre><code>$a = (1 &lt;&lt; 0);
  $b = (1 &lt;&lt; $a);
  $c = (1 &lt;&lt; $b);
  
  echo ($c || $b) &lt;&lt; 2 * $a | $a; //5
  </code></pre>