Documentation missing for Aggregate#out

[Michael Luder-Rosefield]

Looking at the sourcecode, line 251, the $out aggregate operator is added to Aggregate.prototype:

'group match skip limit out'.split(' ').forEach(function($operator) {
   Aggregate.prototype[$operator] = function(arg) {
     var op = {};
     op['$' + $operator] = arg;
     return this.append(op);
   };
 });

There is no mention of this in the docs, however.