# File lib/mutter/mutterer.rb, line 46
    def clear opt = :all
      case opt
        when :user     then @styles = {}
        when :styles   then @styles, @defaults = {}, {}
        when :active   then @active = []
        when :all      then @active, @styles, @defaults = [], {}, {}
        when :default,
             :defaults then @defaults = {}
        else           raise ArgumentError, "[:user, :default, :active, :all] only"
      end
      self
    end