code: function(a, b) {
  		if (a || !b) {
  			var r = {};
  			for (var x in a) {
  				// Does the property not exist?
  				if (!(x in b)) {
  					r[x] = a[x];
  				}
  			}
  
  			return r;
  		}
  
  		return a;
  	}
docs: Get the different hash of properties unique to `a`, and not in `b`