def get_json_ld_extra(key, value):
    '''Serialize an extras key, value pair into JSON-LD'''
    value = value.serialize() if hasattr(value, 'serialize') else value
    return {
        '@type': 'http://schema.org/PropertyValue',
        'name': key,
        'value': value,
    }
Serialize an extras key, value pair into JSON-LD