title: KeyGesture not accepting a Shift+Alphanumeric key combination
body: <p>I'm attempting to execute some WPF commands with help of WPF <code>KeyGesture</code> class. Application works fine until I specify a key combination consisting of <kbd>Shift</kbd> modifier and an alphanumeric key. For example, following instantiation: <code>new KeyGesture(Key.M, ModifierKeys.Shift)</code> throws an exception: </p>
  
  <blockquote>
    <p><strong>'Shift+M' key and modifier combination is not supported for KeyGesture.</strong></p>
  </blockquote>
  
  <p>Bare <kbd>Shift</kbd> modifier won't work with numbers too (e.g. <kbd>Shift</kbd> + <kbd>2</kbd>). However, <kbd>Shift</kbd> + <kbd>Insert</kbd> or <kbd>Shift</kbd> + <kbd>F1</kbd> combinations work flawlessly. Just to put it clear, there are no problems with <kbd>Shift</kbd> + <kbd>Ctrl</kbd>, <kbd>Shift</kbd> + <kbd>Alt</kbd> or <kbd>Alt</kbd> + <kbd>1</kbd> and alike.</p>
  
  <p>Why was a decision made to forbid <kbd>Shift</kbd> + [Alphanumeric] gesture? Does it have anything in common with typing capital letters? Is there a workaround coherent with the WPF commanding system?
  (<em>Note: I'm not trying to use a <kbd>Shift</kbd> + <kbd>M</kbd> gesture, while filling textboxes, but rather when <strong>no</strong> textbox is in focus.</em>)</p>
  
  <p>I seem to find only one forum entry, where this issue is raised. A documentation search failed. Is it so obvious for developers to avoid <kbd>Shift</kbd> + [Alphanumeric]?</p>