- droppable
  accept: function(draggable) {
  return $(draggable).is('.green');
  }
  draggable
  .red
  draggable
  .green
- droppable
  accept: '.little'
  draggable
  .little
  draggable
  .big
- droppable
  activeClass: 'silver'
  draggable
  .gray
- droppable
  droppable
  greedy: false
  draggable
  .orange
- droppable
  droppable
  greedy: true
  draggable
  .purple
- droppable
  hoverClass: 'silver'
  draggable
  .gray
- droppable
  fit
  tolerance: 'fit'
  //100% inside droppable
  draggable
- droppable
  intersect
  tolerance: 'intersect'
  //at least 50% inside droppable
  draggable
- droppable
  pointer
  tolerance: 'pointer'
  //mouse pointer inside droppable
  draggable
  draggable
- droppable
  touch
  tolerance: 'touch'
  //any amount inside droppable
  draggable