Shows this message.

async def _default_help_command(ctx, *commands : str):
    """Shows this message."""
    bot = ctx.bot
    destination = ctx.message.author if bot.pm_help else ctx.message.channel

    def repl(obj):
        return _mentions_transforms.get(obj.group(0), '')

    # help by itself just lists our own commands.
    if len(commands) == 0:
        pages = bot.formatter.format_help_for(ctx, bot)
    elif len(commands) == 1:
        # try to see if it is a cog name
        name = _mention_pattern.sub(repl, commands[0])
        command = None
        if name in [x.lower() for x in bot.cogs]:
            command = bot.cogs[[x for x in bot.cogs if x.lower() == name][0]]
        else:
            command = bot.commands.get(name)
            if command is None:
                await bot.responses.failure(destination=destination, message=bot.command_not_found.format(name))
                return

        pages = bot.formatter.format_help_for(ctx, command)
    else:
        name = _mention_pattern.sub(repl, commands[0])
        command = bot.commands.get(name)
        if command is None:
            await bot.responses.failure(destination=destination, message=bot.command_not_found.format(name))
            return

        for key in commands[1:]:
            try:
                key = _mention_pattern.sub(repl, key)
                command = command.commands.get(key)
                if command is None:
                    await bot.responses.failure(destination=destination, message=bot.command_not_found.format(name))
                    return
            except AttributeError:
                await bot.responses.failure(destination=destination, message=bot.command_has_no_subcommands.format(command, key))
                return

        pages = bot.formatter.format_help_for(ctx, command)

    if bot.pm_help is None:
        characters = sum(map(lambda l: len(l), pages.values()))
        if characters > 1000:
            destination = ctx.message.author

    await bot.responses.full(destination=destination, **pages)