docs: def label_pattern_option_validator(ctx, param, value):
      """Checks that a given string has all the required placeholders. The
      possible placeholders are **{type}**, **{scope}** and **{subject}**.
  
      ``{type}`` are always required, ``{scope}`` is optional and
      ``{subject}`` are required only when ``label_position`` option is set to
      ``header``.
  
      If the pattern is invalid, raises :class:`click.UsageError`.
      """
  
      missings = []
      label_position = ctx.params["label_position"]
  
      if "{type}" not in value:
          missings.append(style("{type}", fg="red", bold=True))
  
      if label_position == "header" and "{subject}" not in value:
          missings.append(style("{subject}", fg="red", bold=True))
  
      if missings:
          message = "\n"
  
          for placeholder in missings:
              message += f"  {x_mark} Missing {placeholder} placeholder.\n"
  
          ctx.fail(message)
  
      return value