anchor.diff:      // force going to active step again, to trigger rescaling
       pres.goto(pres.mCurrentStep);
     }, 250));
  - 
  +
   }
   
   /**
  
positive.code:   num minScale;
    num perspective;
    num transitionDuration;
    
    num getAttribute(Element root, String a, num def) =>
        (root.attributes[a] == null) ?
          def : Math.parseDouble(root.dataset[a]);
    
    Config(Element root)
    {
      height = getAttribute(root,"height",768);
  
negative.code:     s.pos.z = attr('data-z');
      s.rot.x = attr('data-rotate-x');
      s.rot.y = attr('data-rotate-y');
      // Treat data-rotate as data-rotate-z:
      // Allows using only data-rotate for pure 2D rotation
      s.rot.z = attr('data-rotate-z', attr('data-rotate'));
      return s;
    }
  
  