What is expected of the 'folder' parameter for the 'Get Emails' endpoint?

Two related questions:

1) What is required for the ambiguous 'folder' parameter noted here: http://developers.marketo.com/rest-api/endpoint-reference/asset-endpoint-reference/#!/Emails/getEmailUsingGET

JSON formatted ID (from the UI) and folder ID (from the API using http://developers.marketo.com/rest-api/endpoint-reference/asset-endpoint-reference/#!/Folders/getFolderByNameUsingGET​) are not working.

The request returns 711 and 720 errors (not found, invalid folder types) for programs, folders and parent folders that have approved emails in them using the IDs from getFolderByName.

2) What does Marketo want for application/x-www-url-formencoded when using JSON in the query e.g. below?

&folder={"id":1234,"type":"Folder"}