如果 tag（4d3ed089fb60ab534684b7e0）已经嵌入到 post（4d3ed089fb60ab534684b7e9），其他 post 是不是就无法嵌入这个 tag 了？

model

class Post
  include Mongoid::Document
  field :title, :type =>  String
  field :body, :type =>  String
  field :tags, :type =>  Array
  embeds_many :tags
end
class Tag
  include Mongoid::Document  
  field :tag, :type =>  String
  field :type, :type =>  String
  embedded_in :post
end

storage

{
  "_id" : ObjectId("4d3ed089fb60ab534684b7e9"),
  "tags" : [
    {
      "_id" : ObjectId("4d3ed089fb60ab534684b7e0"),
      "name" : "Violator",
    }
  ]
}