def __init__(self, prefix: str, name: str) -> None:
            """Initialize the object.

            `Prefix` should be the common prefix for errors in this group,
            e.g., "D1".
            `name` is the name of the group (its subject).

            """
            self.prefix = prefix
            self.name = name
            self.errors = []  # type: List[ErrorParams]