Skip to main content
MRS-S is an S-expression-based format optimized for complete semantic fidelity, clear hierarchy, readability, straightforward parsing, and stable identity via UUIDs. See: /MRS-Specification-RFC#4-mrs-s-the-canonical-format

​
Top-level Structure

(mrs-s <version>
  (meta <metadata>)
  (parts <part-definitions>)
  (measures <measure-content>)      ; OR (movements <movement-content>)
  (spans <span-definitions>)
  (overlays <overlay-content>)      ; OPTIONAL
  (alternatives <alt-content>)      ; OPTIONAL
  (layout <layout-hints>))          ; OPTIONAL
See: /MRS-Specification-RFC#4-2-document-structure

​
Key Characteristics

​
Stable UUID Identifiers

Every measure, event, and span carries a stable UUIDv7 identifier: 
(measure 
  :id #uuid "018c3f40-1234-7890-abcd-ef1234567890"
  :number 45
  :beat-start 487+1/4
  ...)

(: 0 C5.q 
  :id #uuid "018c3f2a-1234-7890-abcd-ef1234567890"
  :at 487+1/4
  :dyn p)
  • :id — Stable identity for all internal references
  • :number / beat — Display/structural position for human navigation

​
Dual Positioning

Every event has both structural position (beat within measure) and absolute position: 
(: 0 C5.q        ; Beat 0 within measure
  :at 487+1/4    ; Absolute position in quarter-notes
  :id #uuid "...")

​
All References Use UUIDs

Span endpoints, working set scopes, overlay regions—everything references by UUID: 
(slur
  :id #uuid "018c3f2c-..."
  :from #uuid "018c3f2a-..."
  :to #uuid "018c3f2b-...")