title: About override ProcessCMDKey in c# winform
body: <p>I want my app to respond to left arrow and right arrow key.
  So I wrote</p>
  
  <pre><code>protected override bool ProcessCmdKey(ref Message msg, Keys keyData)
  </code></pre>
  
  <p>When I click Ctrl on the left side of the keyboard,
  this function will be called, and the value of keyData is </p>
  
  <pre><code>keyData = LButton | ShiftKey | Control
  </code></pre>
  
  <p>Why is that?</p>
  
  <p>Thank you!</p>