anchor.diff:  
   [discrete]
   ==== `Model` component
  +
  +*Scenario:* You are in charge of `model`. One day, the `logic`-in-charge approaches you for help. He wants to implement a command such that the user is able to remove a particular tag from everyone in the address book, but the model API does not support such a functionality at the moment. Your job is to implement an API method, so that your teammate can use your API to implement his command.
   
   [TIP]
   Do take a look at <<Design-Model>> before attempting to modify the `Model` component.
  
positive.code: [discrete]
  ==== `Logic` component
  
  [TIP]
  Do take a look at <<Design-Logic>> before attempting to modify the `Logic` component.
  
  
negative.code: === Creating a new command: `remark`
  
  By creating this command, you will get a chance to learn how to implement a feature end-to-end, touching all major components of the app.
  
  *Scenario:* You are a software maintainer for `addressbook`, as the former developer team has moved on to new projects. The current users of your application have a list of new feature requests that they hope the software will eventually have. The most popular request is to allow adding additional comments/notes about a particular contact, by providing a flexible `remark` field for each contact, rather than relying on tags alone. After designing the specification for the `remark` command, you are convinced that this feature is worth implementing. Your job is to implement the `remark` command.
  
  ==== Description
  Edits the remark for a person specified in the `INDEX`. +
  