class AcceptCharsetHeaderTransform < HeaderTransform
      rule(charset: simple(:c), q: simple(:q)) { CharsetRange.new(c, q) }
      rule(charset: simple(:c)) { CharsetRange.new(c) }
      rule(accept_charset: sequence(:cr)) { Headers::AcceptCharset.new(*cr) }
      rule(accept_charset: simple(:cr)) { Headers::AcceptCharset.new(cr) }