Every entity in FiFo's database can have metadata attached to it. This metadata is ignored by FiFo itself but an be leveraged by any software that integrates with it. The metadata is represented as a JSON object, nested keys can be directly accessed by using the URL to specify the path.
As a convention metadata should never be written to a the root key but should be prefixed with an identifier of the application using it. In the example code we set the notes to be displayed in cerberus so the the key is cerberus.notes (as seen by the URL path of /metadata/cerberus. This best practice prevents conflicts between applications that might want to use the same names for different kinds of metadata.
Metadata generally should be kept small, a few kilobyte as most as larger metadata can have a negative impact on the performance of the overall system!