flatspan.rb

#!/usr/bin/env ruby
# coding: utf-8
require 'rexml/document'
include REXML
doc = Document.new(ARGF)
doc.context[:attribute_quote] = :quote

# 親spanを追加するには%w()内に空白区切りで指定
%w(bold).each do |style|
  doc.each_element("//span[@class='#{style}']") do |e|
    e.each do |ec|
      if ec.class == Text
        ec.parent.insert_after(ec, Document.new("<span class=\"#{style}\">#{ec}</span>", {:attribute_quote => :quote}))
        ec.remove
      elsif ec.class == Element && ec.name == 'span' && ec.attributes['class']
        ec.attributes['class'] = "#{style} #{ec.attributes['class']}"
      end
    end
    e.name = 'removeme'
  end
end

puts doc.to_s.gsub(/<[\/]?removeme.*?>/, '')