You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: mspec-tag.rb
    path of file: ./repos/ferrocarril/spec-runner/spec/mspec/lib/mspec/commands
    
    the code of the file until where you have to start completion: #!/usr/bin/env 
    
  def register
    require 'mspec/runner/actions'

    case config[:tagger]
    when :add, :del
      tag = SpecTag.new config[:tag]
      tagger = TagAction.new(config[:tagger], config[:outcome], tag.tag, tag.comment,
                             config[:atags], config[:astrings])
    when :list, :list_all
      tagger = TagListAction.new config[:tagger] == :list_all ? nil : config[:ltags]
      MSpec.register_mode :pretend
      config[:formatter] = false
    when :purge
      tagger = TagPurgeAction.new
      MSpec.register_mode :pretend
      MSpec.register_mode :unguarded
      config[:formatter] = false
    else
      raise ArgumentError, "No recognized action given"
    end