rough draft

docs/general/passing_arbitrary_options.md

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+## Passing Arbitrary Options to A Serializer
+
+Let's say you have a basic Post Controller:
+
+```
+class PostController < ApplicationController
+  def dashboard  
+    render json: @posts
+  end
+end
+```
+
+Odds are, your serializer will look something like this:
+
+```
+class PostSerializer < ActiveModel::Serializer
+  attributes :id, :title, :body
+end
+```
+
+This works all fine and well, but maybe you passing in some "artibrary" options
+into the serializer. Here's what you would do:
+
+### posts_controller.rb
+
+```
+...
+  def dashboard  
+    render json: @posts, user_id: 12
+  end
+...
+```
+
+### posts_serializer.rb
+
+```
+...
+  def comments_by_me  
+    Comments.where(user_id: instance_options[:user_id], post_id: object.id)
+  end
+...
+```
+
+These options can be anything that isn't already reserved for use by AMS. For example,
+you won't be able to pass in a `meta` or `root` option like the example above. Those
+parameters are reserved for specific behavior within the app.