Sourceval to_value :
Item.t list->[> `List of
[> `Structure of
(string
* [> `Enum of string| `List of
[> `Structure of
(string * [> `Enum of string| `String of ContentType.t ])
list ]
list| `String of Instant.t| `Structure of
(string
* [> `Enum of string| `List of
[> `Structure of
(string * [> `String of Instant.t ]) list ]
list| `String of ChatItemId.t ])
list ])
list ]
list ]