Unique1ID
ResType rType ; 4-byte resource type; e.g., 'MENU' returns a resource ID, unique with respect to current file
Unique1ID returns a unique, unused resource ID that will not collide with any resource of the specified type in the current resource file.
rType is a 4-byte ResType value. It identifies the resource type for which you wish a unique resource ID (e.g., 'FONT', 'WIND', etc.)
Returns: an integer; a resource ID number that is unique with respect to resources of type rType in the current resource file.
Notes: This function is the "1-deep" version of UniqueID. It generates a resource ID that is unique with respect to resources in the current resource