Does anyone know whether it's possible to set a start node and / or allowed document type for the content picker setting type.

I'm creating a custom workflow and have a setting that uses the Pickers.Content type. Ideally I would like to limit the content or at least the document type users can select however I don't know whether this is possible or how to do it.

The following is my setting code.

[Setting("Email Template", Description = "Select the email template.", View = "Pickers.Content")]

Does anyone know whether it's possible, either from passing prevalues or from some other way of setting which node I want the content picker to start from and / or limiting the document types that can be selected using it.