It improving validation on droping node in specified role.
With new code you can validate nodes by attributes from chef object in realtime by using validators: include, expr, le, eq, ge, ne.

Example for barclamps: (crowbar_framework/app/views/barclamp/<barclamp>/_edit_deployment.html.haml)
$(document).ready(function(){
  var constraints = {  
    "some-role": { attributes: {"cpu/total": {le: 2} } }
  };
  node_selector($('#drag_drop'), constraints);
});
This code not allow drop node to role some-role when node has only 2 CPUs.