Raise a ValueError if DATA doesn't seem to be a well-formed ID3 tag.

def check_tag_data(data):
    "Raise a ValueError if DATA doesn't seem to be a well-formed ID3 tag."
    if len(data) < 10:
        raise ValueError("Tag too short")
    if data[0:3] != b"ID3":
        raise ValueError("Missing ID3 identifier")
    if data[3] >= 5 or data[4] != 0:
        raise ValueError("Unknown ID3 version")
    length = stagger.conversion.Syncsafe.decode(data[6:10]) + 10
    if len(data) != length:
        raise ValueError("Tag size mismatch")