title: key press event in qt
body: <p>I wonder is there any difference between <code>Qt::ShiftModifier</code> and <code>Qt::Key_Shift</code>?
  And what the difference between :</p>
  
  <pre><code>if(event-&gt;modifiers() &amp; Qt::ShiftModifier){...}
  </code></pre>
  
  <p>and</p>
  
  <pre><code>if(event-&gt;modifiers() == Qt::ShiftModifier){...}
  </code></pre>