1.7 Vendor-Extensible Fields
File system control codes that are used to set reparse point data specify a ReparseTag field value that identifies the file system filter that understands the application-specific reparse point data format. A vendor developing an application protocol that sets reparse point data should request a unique reparse tag for that application from Microsoft by following the instructions described in [WHDC-RPTR]. For more information about reparse points, see [REPARSE].
This protocol uses NTSTATUS values, as specified in [MS-ERREF]. Vendors are free to choose their own values for this field as long as the C bit (0x20000000) is set, indicating it is a customer code.