code: def __format_occurence(self, occurence):
          
  
          color = "rgb({0}, {1}, {2})"
          span_format = "<span style=\"color: {0};\">{{0}}</span>".format(color.format(self.__default_line_color.red(),
                                                                                       self.__default_line_color.green(),
                                                                                       self.__default_line_color.blue()))
          line = foundations.strings.to_string(occurence.text)
          start = span_format.format(line[:occurence.column])
          pattern = "<b>{0}</b>".format(line[occurence.column:occurence.column + occurence.length])
          end = span_format.format(line[occurence.column + occurence.length:])
          return "".join((start, pattern, end))
docs: Formats the given occurence and returns the matching rich html text.
  
          :param occurence: Occurence to format.
          :type occurence: Occurence
          :return: Rich text.
          :rtype: unicode