'Delete all values associated with the key.'

def __delitem__(self, key):

    if isinstance(key, slice):
        return VComment.__delitem__(self, key)
    if (not is_valid_key(key)):
        raise ValueError
    key = key.lower()
    to_delete = [x for x in self if (x[0].lower() == key)]
    if (not to_delete):
        raise KeyError(key)
    else:
        for item in to_delete:
            self.remove(item)
