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MRS-S is the canonical storage format for complete, archival-quality scores. It is optimized for semantic fidelity, human readability, and validation. See: /MRS-Specification-RFC#4-mrs-s-the-canonical-storage-format

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Role in MRS Architecture

FormatPurpose
MRS-SStorage, interchange, agent input
MRS-OpsAgent output, mutations
Agents read MRS-S fragments in Working Set Envelopes. Agents write MRS-Ops operations. The orchestrator applies operations to canonical score state.

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Top-level Structure

(mrs-s 1.0
  (meta <metadata>)
  (players <player-definitions>)
  (instruments <instrument-definitions>)
  (measures <measure-content>)           ; OR (movements <movement-content>)
  (spans <span-definitions>)
  (overlays <overlay-content>)           ; OPTIONAL
  (structural-index <index-content>)     ; OPTIONAL
  (alternatives <alt-content>)           ; OPTIONAL
  (layout <layout-hints>))               ; OPTIONAL

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Key Characteristics

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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
  ...)

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

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Player-Instrument Model

Players own instruments; instruments appear in measure content: 
(players
  (player woodwind-2
    :name "Flute 2 / Piccolo"
    :instruments [flute-2 piccolo]
    :default flute-2))

(instruments
  (instrument flute-2 :name "Flute" :transposition none ...)
  (instrument piccolo :name "Piccolo" :transposition (up P8) ...))

(measures
  (measure :id #uuid "..." :number 1
    (flute-2 (v1 ...))    ; Before instrument change
    (piccolo (v1 ...))))  ; After instrument change

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Orchestrator-Computed Derived Fields

In MRS-S storage, :at (absolute position) is optional. The orchestrator computes it: 
event.:at = measure.:beat-start + event.beat
This is a change from earlier versions: agents no longer provide :at in operations; the orchestrator computes it.

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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-...")

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Canonical Rational Syntax

All temporal positions use exact rationals: 
0, 1, 2              ; Integers
2+1/2                ; Two and a half
0+1/3                ; One third
3+3/4                ; Three and three quarters
Decimal literals (2.5) are NOT permitted.

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File Types

  • MIME type: application/vnd.mrs+sexpr
  • Extensions: .mrs or .mrs-s
  • Encoding: UTF-8 (no BOM)