text: // Make sure we only make a DBRef object for objects where the first field is a string named $ref
  // and the second field is $id with any type. Only the first two fields matter for deciding if it
  // is a DBRef. See http://docs.mongodb.org/manual/reference/database-references/#dbrefs.
  
  var t = db.dbref3;
  
  t.drop();
  
  // true cases
  t.insert({sub: {$ref: "foo", $id: "bar"}, dbref: true});
  t.insert({sub: {$ref: "foo", $id: "bar", $db: "baz"}, dbref: true});
  t.insert({sub: {$ref: "foo", $id: "bar", db: "baz"}, dbref: true}); // out of spec but accepted
  t.insert({sub: {$ref: "foo", $id: ObjectId()}, dbref: true});
  t.insert({sub: {$ref: "foo", $id: 1}, dbref: true});
  
  t.insert({sub: {$ref: 123/*not a string*/, $id: "bar"}, dbref: false});
  t.insert({sub: {$id: "bar", $ref: "foo"}, dbref: false});
  t.insert({sub: {$ref: "foo"}, dbref: false});
  t.insert({sub: {$id: "foo"}, dbref: false});
  t.insert({sub: {other: 1, $ref: "foo", $id: "bar"}, dbref: false});
  
  t.find().forEach(function(obj) {
      assert.eq(obj.sub.constructor == DBRef, obj.dbref, tojson(obj));
  });
  
  // We should be able to run distinct against DBRef fields.
  var distinctRefs = t.distinct('sub.$ref');
  print('distinct $ref = ' + distinctRefs);
  
  var distinctIDs = t.distinct('sub.$id');
  print('distinct $id = ' + distinctIDs);
  
  var distinctDBs = t.distinct('sub.$db');
  print('distinct $db = ' + distinctDBs);
  
  // Confirm number of unique values in each DBRef field.
  assert.eq(2, distinctRefs.length);
  assert.eq(4, distinctIDs.length);
  assert.eq(1, distinctDBs.length);
  
  // $id is an array. perform positional projection on $id.
  t.insert({sub: {$ref: "foo", $id: [{x: 1, y: 1}, {x: 2, y: 2}, {x: 3, y: 3}]}});
  var k = t.findOne({'sub.$id': {$elemMatch: {x: 2}}}, {_id: 0, 'sub.$id.$': 1});
  print('k = ' + tojson(k));
  assert.eq({sub: {$id: [{x: 2, y:2}]}}, k);