singleton types

[amitu]

Sometimes we want to store some data about the document. Such data must only be present once in the document. Some types can be marked as singleton to force ftd to only allow one such instance per document. The instance may even be anonymous.

-- record person:
$singleton$: true
caption name:

-- person: Amit Upadhyay

If you want to use the person data in rest of the current document you can do bind it to a name.

If you want to access such data from other documents you can either use the package query mechanism or bind them to a name (do not create anonymous instance).

Once type alias is implemented we can even make other types singleton:

-- type title: string
$singleton$: true

Now we have created a type called title and it is marked singleton, but it is just a string.

Challenge

In a document that queries such records defined in other documents, do we still enforce singleton rule?