HL7's Payer/Provider Information Exchange Work Group (PIE) — formerly the Attachments WG; the public URL still says "claims" — owns provider↔payer supplemental-information exchange: claims attachments and attachment patterns for eligibility, prior auth, and referrals. It works jointly with X12 on attachment transactions and with Regenstrief on LOINC attachment codes.

This committee's charter got louder when CMS published CMS-0053-F (March 2026): HIPAA standards for claims attachments pairing X12N 275/277 transport with HL7 C-CDA / Attachments IG content. Every plan that just planned CMS-0057 prior-auth work now has a second interop mandate on a nearby timeline. Attachments are supporting documentation — the same evidence problem PAS/DTR/CDex target on the FHIR path.

What ImOnFHIR does with it: we use PIE and CMS pages as comply-track headlines ("your next two mandates") and watch for the FHIR/CDex attachments path versus the X12/C-CDA baseline. We note X12 275 as a future inbound shape for attachment metadata; we do not host licensed X12 specs or CPT content.