'A list of values for the key.
This is a copy, so comment[\'title\'].append(\'a title\') will not
work.'

def __getitem__(self, key):

    if isinstance(key, slice):
        return VComment.__getitem__(self, key)
    if (not is_valid_key(key)):
        raise ValueError
    key = key.lower()
    values = [value for (k, value) in self if (k.lower() == key)]
    if (not values):
        raise KeyError(key)
    else:
        return values
