code: def add_line(self, line):
          
          if not self.is_valid_line(line):
              logger.warn(
                  "Invalid line for %s section: '%s'",
                  self.section_name, line
              )
              return
  
          self.lines.append(line)
docs: Adds a given line string to the list of lines, validating the line
          first.