def fixed length, options = {}
      options[:zero] = true if options[:zero].nil?
      NationalSplitters::Fixed.instance_for length, options
    end
def fixed length, options = {}
      options[:zero] = true if options[:zero].nil?
      NationalSplitters::Fixed.instance_for length, options
    end
National matcher & splitters.

 By default, a fixed length NDC
 uses a zero prefix when formatted
 with format :national.

 @param [Fixnum] length The length of the fixed length NDC.
 @param [Hash] options An options hash (set zero: false to not add a zero on format :national).

 @return NationalSplitters::Fixed A fixed length national splitter.

 @example France. Uses a fixed NDC of size 1.
   country '33', fixed(1) >> split(2,2,2,2)