def is_link(value):
    """
    Checks if value is link or not.

    :param value: any object.
    :return: Boolean
    :rtype: bool

    Usage:
        >>> is_link('foo')
        False
        >>> is_link({'sys': {'type': 'Link', 'id': 'foobar'}})
        True
    """
    return isinstance(value, dict) and value.get('sys', {}).get('type', ''
        ) == 'Link'
