title: How to exclude multiple physicsbody collisionBitMask
body: <p>I found from other SO' answer that you can exclude collisions btw same type of spritenode's physicsbody, by using ~ in the bitmask like so:</p>
  
  <pre><code>    self.physicsBody = [SKPhysicsBody bodyWithCircleOfRadius:self.size.width/2.0];
      self.minionLife = 1.0;
      self.minionSpeed = 60.0;
      self.minionPath = 0;
      self.physicsBody.categoryBitMask = cat_enemy1;
  
      // does not collide with itself
      self.physicsBody.collisionBitMask = ~cat_enemy1; // here
  </code></pre>
  
  <p>Question is how to add more exclusions to this collisionBitMask?</p>
  
  <p>I tried:</p>
  
  <pre><code>self.physicsBody.collisionBitMask = ~cat_enemy1 | ~cat_playerShip; // here
  </code></pre>
  
  <p>But not working.</p>