gistfile1.js

var matchers = [
  { $ref: 'one_post',
    id: {$index: true},
    type: 'post'
  },
  { $ref: 'many_comments',
    postId: {$index: true},
    type: 'comment'
  },
]

var postId = 'post-1'

createMatchStream([
  {$ref: 'one_post', id: postId}, 
  {$ref: 'many_comments', postId: postId}
])

or.js

var matchers = [
  { $ref: 'one_post',
    $index: ['id']
    type: 'post'
  },
  { $ref: 'many_comments',
    $index: ['postId']
    type: 'comment'
  },
]

var postId = 'post-1'

createMatchStream([
  {$ref: 'one_post', id: postId}, 
  {$ref: 'many_comments', postId: postId}
])