def qvalue(charset)
      m = matches(charset)
      if m.empty?
        charset == 'iso-8859-1' ? 1 : 0
      else
        normalize_qvalue(@qvalues[m.first])
      end
    end
def qvalue(charset)
      m = matches(charset)
      if m.empty?
        charset == 'iso-8859-1' ? 1 : 0
      else
        normalize_qvalue(@qvalues[m.first])
      end
    end
Determines the quality factor (qvalue) of the given +charset+.