REST API - when I get the metadata for a record, is it possible to programatically see what object types are referenced by custom fields on that record? Example -- I've got a SalesOrder with a custom field custbody_foo, with enum values 1,2,3,4. custbody_foo is a List/Record field type, but the API doesn't appear to tell me what List/Record to look up to find the meaning of the enum values