title: How does work touchBegin on SKSpriteNode(SKNode) on SpriteKit?
body: <p>I use SpriteKit with Swift. A button I realized by override touchesBegin on SKSpriteNode. But I don't understand how it catch touch. Sometimes button not catch if over it has SKSpriteNode and sometimes on the contrary. Please explain to me.</p>
  
  <p>Thanks!</p>