title: How to deal with a Toggle NSButton?
body: <p>My application contains a PLAY/PAUSE button that is set to type <em>Toggle</em> in Interface Builder. I use it - as the name reveals - to play back my assets or to pause them.<br>
  Further, I am listening to the SPACE key to enable the same functionality via the keyboard shortcut. Therefore, I use <code>keyDown:</code> from <code>NSResponder</code>in my application. This is done in another subview. The button itself is not visible at this time.<br>
  I store the current state of playback in a Singleton.</p>
  
  <p>How would you update the title/alternative title for the toogle button while taking into account that its state could have been altered by the keyboard shortcut? Can I use bindings?</p>