Parse an item (and more specifically its key).

def parse_item(self, key, value, flags: Flags) -> Optional[TransItem]:
        """
        Parse an item (and more specifically its key).
        """

        parts = key.split('+')
        pure_key = parts[0]

        try:
            if len(parts) == 2:
                index = int(parts[1])
            elif len(parts) > 2:
                return
            else:
                index = 1
        except (ValueError, TypeError):
            return

        if index < 1:
            return

        return TransItem(
            key=pure_key,
            index=index,
            value=value,
            flags=flags,
        )