# 260614 — Project Xanadu deep dive (the docuverse, the EDL, reference-not-copy)

Date: 2026-06-14

## What this is

A focused study of **Project Xanadu** (Ted Nelson) read through shard-wiki's lens.
Unlike the engine dives (`xwiki`, `twiki`, `foswiki`), Xanadu is **not a candidate
shard backend** — it never shipped at scale and there is nothing to attach. It is
studied as the **deepest conceptual ancestor** of shard-wiki's own model: several
shard-wiki primitives turn out to be Xanadu mechanisms under different names.

The distinctive material:
- the **EDL / xanadoc** — a document that contains *no content*, only an ordered list
  of **spans** (content references) plus **xanalinks** (separate link tables); the
  client assembles the page by reference → this is shard-wiki **projection** + **union**
- the storage substrate — **tumblers** (stable fine-grained addresses), **istream**
  (invariant content pool), **enfilades / spanfilade** (virtual↔content mapping,
  version comparison by span-set intersection)
- **content-identity, bidirectional transclusion** — content "knowably in more than
  one place" that remembers all its appearances → stronger than UC-32
- **transcopyright / micropayment** — a baked-in rights policy shard-wiki must keep
  *configurable*, not inherit

Goes deliberately **underneath** the surface pattern table in
`research/260608-federation-concepts/findings.md` §3.3, which it extends rather than
repeats.

## Contents

| Path | Role |
|------|------|
| `findings.md` | EDL/xanadoc, addressing substrate, transclusion, versioning, rights, INTENT mapping (reinforcements + design-bug divergences), UC seeds, architecture notes, sources |

## Status

Initial deep dive complete. Three new use cases promoted to `spec/UseCaseCatalog.md`
(UC-44 compose-by-reference, UC-45 reverse transclusion, UC-46 content-identity
equivalence); UC-24/27/29/32 enriched. Span-addressing as an adapter capability,
content identity, composition manifests, and reuse-terms metadata logged as
architecture for `workplans/SHARD-WP-0002-federation-architecture.md`.

Key boundary recorded: shard-wiki inherits Xanadu's **reference-not-copy** mechanisms
but **rejects** the single-global-docuverse premise, the single-canonical-instance
model, and the baked-in economic policy — those would violate shard sovereignty,
parallel-version support (UC-27), and mechanism-over-policy.
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