docs: def help_handler(docpie, flag):
          """Default help(`--help`, `-h`) handler. print help string and exit.
  
          when help = 'short_brief', flag startswith `--` will print
          the full `doc`, `-` for "Usage" section and "Option" section only.
          when help = 'short_brief_notice', flag startswith `--` will print
          the full `doc`, `-` for "Usage" section and "Option" section only,
          with a message.
          "Use `--help` to see the full help messsage" in the end
  
          otherwith(default), print the full `doc`
          """
          help_type = docpie.help
          helpstyle = docpie.helpstyle
          if helpstyle == 'python':
              doc = Docpie.help_style_python(docpie.doc)
          elif helpstyle == 'dedent':
              doc = Docpie.help_style_dedent(docpie.doc)
          # elif help_style == 'raw':
          #     doc = Docpie.help_style_raw(docpie.doc)
          else:
              doc = docpie.doc
  
          if help_type == 'short_brief':
              if flag.startswith('--'):
                  print(doc)
              else:
                  print(docpie.usage_text.rstrip())
                  option_sections = docpie.option_sections
                  if option_sections:
                      print('')
                      print('\n'.join(option_sections.values()))
          elif help_type == 'short_brief_notice':
              if flag.startswith('--'):
                  sys.stdout.write(doc)
              else:
                  print(docpie.usage_text)
                  option_sections = docpie.option_sections
                  if option_sections:
                      print('')
                      print('\n'.join(option_sections.values()).rstrip())
                  print('')
                  print('Use `--help` to see the full help messsage.')
          else:
              sys.stdout.write(doc)
          sys.exit()