def qvalue(encoding)
      m = matches(encoding)
      if m.empty?
        encoding == 'identity' ? 1 : 0
      else
        normalize_qvalue(@qvalues[m.first])
      end
    end
def qvalue(encoding)
      m = matches(encoding)
      if m.empty?
        encoding == 'identity' ? 1 : 0
      else
        normalize_qvalue(@qvalues[m.first])
      end
    end
Determines the quality factor (qvalue) of the given +encoding+.