def merge0(oth)
      oth = parser.send(:convert_to_uri, oth)

      if self.relative? && oth.relative?
        raise BadURIError,
          "both URI are relative"
      end

      if self.absolute? && oth.absolute?
        #raise BadURIError,
        #  "both URI are absolute"
        # hmm... should return oth for usability?
        return oth, oth
      end

      if self.absolute?
        return self.dup, oth
      else
        return oth, oth
      end
    end
def merge0(oth)
      oth = parser.send(:convert_to_uri, oth)

      if self.relative? && oth.relative?
        raise BadURIError,
          "both URI are relative"
      end

      if self.absolute? && oth.absolute?
        #raise BadURIError,
        #  "both URI are absolute"
        # hmm... should return oth for usability?
        return oth, oth
      end

      if self.absolute?
        return self.dup, oth
      else
        return oth, oth
      end
    end
return base and rel.
 you can modify `base', but can not `rel'.