decode_www_form

# File lib/uri/common.rb, line 968
  def self.decode_www_form(str, enc=Encoding::UTF_8, separator: '&', use__charset_: false, isindex: false)
    raise ArgumentError, "the input of #{self.name}.#{__method__} must be ASCII only string" unless str.ascii_only?
    ary = []
    return ary if str.empty?
    enc = Encoding.find(enc)
    str.b.each_line(separator) do |string|
      string.chomp!(separator)
      key, sep, val = string.partition('=')
      if isindex
        if sep.empty?
          val = key
          key = ''
        end
        isindex = false
      end

      if use__charset_ and key == '_charset_' and e = get_encoding(val)
        enc = e
        use__charset_ = false
      end

      key.gsub!(/\+|%\h\h/, TBLDECWWWCOMP_)
      if val
        val.gsub!(/\+|%\h\h/, TBLDECWWWCOMP_)
      else
        val = ''
      end

      ary << [key, val]
    end
    ary.each do |k, v|
      k.force_encoding(enc)
      k.scrub!
      v.force_encoding(enc)
      v.scrub!
    end
    ary
  end