title: Built-in WPF IValueConverters
body: <p>Ok, it was a nice surprise (after writing it several times) to find that there already is a <strong>BooleanToVisibilityConverter</strong> in <em>System.Windows.Controls</em> namespace. </p>
  
  <p>Probably there are more such hidden time-savers. </p>
  
  <p>Anyone got some?</p>