Custom metadata in 'key = value' pairs, each key/value pair must be on it's own line so for more than one entry you will need to expand the entry field. Each key must be unique. Each value must be no more than 50 characters.

If you need to add additional metadata, it's strongly recommended that you prefix these properties with an underscore (_) on the off-chance that a property you add will exist in a future version of the specification.