class Differ::Diff

def insert(*str)
  return if str.empty?
  if @raw.last.is_a? Change
    change = @raw.pop
    if change.delete? && @raw.last
      @raw.last << sep if change.delete.sub!(/^#{Regexp.quote(sep)}/, '')
    end
    change.insert << sep if change.insert?
  else
    change = Change.new(:insert => @raw.empty? ? '' : sep)
  end
  @raw << change
  @raw.last.insert << str.join(sep)
end