resource_id
Description:
The resource ID of the document.
This should not normally need to be used in client code, and is mostly for internal use. To uniquely identify a given document or folder, use its id.
Resource IDs have the form: document|drawing|pdf|spreadsheet|presentation|folder:untyped resource ID; whereas entry IDs have the form: https://docs.google.com/feeds/id/resource ID in version 3 of the API.
For more information, see the Google Documents API reference.