anchor.diff:  a particular class for documentation purposes.
   Use `Workflow::create_workflow_diagram(class)` in your rake task like:
   
  -    namespace :doc do
  -      desc "Generate a workflow graph for a model passed e.g. as 'MODEL=Order'."
  -      task :workflow => :environment do
  -        require 'workflow/draw'
  -        Workflow::Draw::workflow_diagram(ENV['MODEL'].constantize)
  -      end
  -    end
  -
  +```rb
  +namespace :doc do
  +  desc "Generate a workflow graph for a model passed e.g. as 'MODEL=Order'."
  +  task :workflow => :environment do
  +    require 'workflow/draw'
  +    Workflow::Draw::workflow_diagram(ENV['MODEL'].constantize)
  +  end
  +end
  +```
   
   
   Changelog
  
positive.code: You can also check, whether a state comes before or after another state (by the
  order they were defined):
  
      article.current_state
      => being_reviewed
      article.current_state < :accepted
      => true
      article.current_state >= :accepted
      => false
      article.current_state.between? :awaiting_review, :rejected
      => true
  
  Now we can call the submit event, which transitions to the
  <tt>:awaiting_review</tt> state:
  
      article.submit!
      article.awaiting_review? # => true
  
  Events are actually instance methods on a workflow, and depending on the
  state you're in, you'll have a different set of events used to
  
negative.code: Workflow::TransitionHalted exception. You can provide an additional
  `halted_because` parameter.
  
  ```rb
  def reject(reason)
    halt! 'We do not reject articles unless the reason is important' \
      unless reason =~ /important/i
  end
  ```
  
  The traditional `halt` (without the exclamation mark) is still supported
  too. This just prevents the state change without raising an
  