docs: update spec page to match latest version and sections

Author: johannschopplich

docs/reference/spec.md

@@ -9,75 +9,91 @@ You don't need this page to *use* TOON. It's mainly for implementers and contrib
 
 ## Current Version
 
-**Spec v{{ $spec.version }}** (2025-11-24) is the current stable version.
+**Spec v{{ $spec.version }}** (2025-11-24) is the current published Working Draft. It is stable for implementation but not yet finalized; see "Status of This Document" in the spec for details.
 
-The spec defines a provisional media type and file extension in §18.2:
+## Media Type & File Extension
 
-- **Media type:** `text/toon` (provisional, UTF-8 only)
+The spec defines a provisional media type and file extension in [§18.2](https://github.com/toon-format/spec/blob/main/SPEC.md#182-provisional-media-type):
+
+- **Media type:** `text/toon` (provisional, not yet IANA‑registered; UTF‑8 only)
 - **File extension:** `.toon`
 
+TOON documents are always UTF‑8 with LF (`\n`) line endings; the optional `charset` parameter, when present, MUST be `utf-8` per the spec.
+
 ## Guided Tour of the Spec
 
 ### Core Concepts
 
-**[§1 Terminology and Conventions](https://github.com/toon-format/spec/blob/main/SPEC.md#1-terminology-and-conventions)**
+[§1 Terminology and Conventions](https://github.com/toon-format/spec/blob/main/SPEC.md#1-terminology-and-conventions):
 Defines key terms like "indentation level", "active delimiter", "strict mode", and RFC2119 keywords (MUST, SHOULD, MAY).
 
-**[§2 Data Model](https://github.com/toon-format/spec/blob/main/SPEC.md#2-data-model)**
+[§2 Data Model](https://github.com/toon-format/spec/blob/main/SPEC.md#2-data-model):
 Specifies the JSON data model (objects, arrays, primitives), array/object ordering requirements, and canonical number formatting (no exponent notation, no leading/trailing zeros).
 
-**[§3 Encoding Normalization](https://github.com/toon-format/spec/blob/main/SPEC.md#3-encoding-normalization-reference-encoder)**
+[§3 Encoding Normalization](https://github.com/toon-format/spec/blob/main/SPEC.md#3-encoding-normalization-reference-encoder):
 Defines how non-JSON types (Date, BigInt, NaN, Infinity, undefined, etc.) are normalized before encoding. Required reading for encoder implementers.
 
-**[§4 Decoding Interpretation](https://github.com/toon-format/spec/blob/main/SPEC.md#4-decoding-interpretation-reference-decoder)**
+[§4 Decoding Interpretation](https://github.com/toon-format/spec/blob/main/SPEC.md#4-decoding-interpretation-reference-decoder):
 Specifies how decoders map text tokens to host values (quoted strings, unquoted primitives, numeric parsing with leading-zero handling). Decoders default to strict mode (`strict = true`) in the reference implementation; strict-mode errors are enumerated in §14.
 
 ### Syntax Rules
 
-**[§5 Concrete Syntax and Root Form](https://github.com/toon-format/spec/blob/main/SPEC.md#5-concrete-syntax-and-root-form)**
+[§5 Concrete Syntax and Root Form](https://github.com/toon-format/spec/blob/main/SPEC.md#5-concrete-syntax-and-root-form):
 Defines TOON's line-oriented, indentation-based notation and how to determine whether the root is an object, array, or primitive.
 
-**[§6 Header Syntax](https://github.com/toon-format/spec/blob/main/SPEC.md#6-header-syntax-normative)**
+[§6 Header Syntax](https://github.com/toon-format/spec/blob/main/SPEC.md#6-header-syntax-normative):
 Normative ABNF grammar for array headers: `key[N<delim?>]{fields}:`. Specifies bracket segments, delimiter symbols, and field lists.
 
-**[§7 Strings and Keys](https://github.com/toon-format/spec/blob/main/SPEC.md#7-strings-and-keys)**
+[§7 Strings and Keys](https://github.com/toon-format/spec/blob/main/SPEC.md#7-strings-and-keys):
 Complete quoting rules (when strings MUST be quoted), escape sequences (only `\\`, `\"`, `\n`, `\r`, `\t` are valid), and key encoding requirements.
 
-**[§8 Objects](https://github.com/toon-format/spec/blob/main/SPEC.md#8-objects)**
+[§8 Objects](https://github.com/toon-format/spec/blob/main/SPEC.md#8-objects):
 Object field encoding (key: value), nesting rules, key order preservation, and empty object handling.
 
-**[§9 Arrays](https://github.com/toon-format/spec/blob/main/SPEC.md#9-arrays)**
+[§9 Arrays](https://github.com/toon-format/spec/blob/main/SPEC.md#9-arrays):
 Covers all array forms: primitive (inline), arrays of objects (tabular), mixed/non-uniform (list), and arrays of arrays. Includes tabular detection requirements.
 
-**[§10 Objects as List Items](https://github.com/toon-format/spec/blob/main/SPEC.md#10-objects-as-list-items)**
-Indentation rules for objects appearing in list items (first field on hyphen line, nested object rules).
+[§10 Objects as List Items](https://github.com/toon-format/spec/blob/main/SPEC.md#10-objects-as-list-items):
+Indentation rules for objects appearing in list items (first field on the hyphen line), including the canonical pattern when the first field is a tabular array (header on the hyphen line, rows at depth +2, sibling fields at depth +1).
 
-**[§11 Delimiters](https://github.com/toon-format/spec/blob/main/SPEC.md#11-delimiters)**
+[§11 Delimiters](https://github.com/toon-format/spec/blob/main/SPEC.md#11-delimiters):
 Delimiter scoping (document vs active), delimiter-aware quoting, and parsing rules for comma/tab/pipe delimiters.
 
-**[§12 Indentation and Whitespace](https://github.com/toon-format/spec/blob/main/SPEC.md#12-indentation-and-whitespace)**
+[§12 Indentation and Whitespace](https://github.com/toon-format/spec/blob/main/SPEC.md#12-indentation-and-whitespace):
 Encoding requirements (consistent spaces, no tabs in indentation, no trailing spaces/newlines) and decoding rules (strict vs non-strict indentation handling).
 
 ### Conformance and Validation
 
-**[§13 Conformance and Options](https://github.com/toon-format/spec/blob/main/SPEC.md#13-conformance-and-options)**
-Defines conformance classes (encoder, decoder, validator), required options, and conformance checklists.
+[§13 Conformance and Options](https://github.com/toon-format/spec/blob/main/SPEC.md#13-conformance-and-options):
+Defines conformance classes (encoder, decoder, validator), standardized options, and conformance checklists.
 
-**[§13.4 Key Folding and Path Expansion](https://github.com/toon-format/spec/blob/main/SPEC.md#134-key-folding-and-path-expansion)**
-Optional encoder feature (key folding) and decoder feature (path expansion) for collapsing/expanding dotted paths. Specifies safety requirements and conflict resolution.
+[§13.4 Key Folding and Path Expansion](https://github.com/toon-format/spec/blob/main/SPEC.md#134-key-folding-and-path-expansion):
+Optional encoder feature (key folding) and decoder feature (path expansion) for collapsing/expanding dotted paths, with deep-merge semantics and strict/non-strict conflict resolution.
 
-**[§14 Strict Mode Errors and Diagnostics](https://github.com/toon-format/spec/blob/main/SPEC.md#14-strict-mode-errors-and-diagnostics-authoritative-checklist)**
+[§14 Strict Mode Errors and Diagnostics](https://github.com/toon-format/spec/blob/main/SPEC.md#14-strict-mode-errors-and-diagnostics-authoritative-checklist):
 **Authoritative checklist** of all strict-mode errors: array count mismatches, syntax errors, indentation errors, structural errors, and path expansion conflicts.
 
 ### Implementation Guidance
 
-**[§19 TOON Core Profile](https://github.com/toon-format/spec/blob/main/SPEC.md#19-toon-core-profile-normative-subset)**
+[§15 Security Considerations](https://github.com/toon-format/spec/blob/main/SPEC.md#15-security-considerations):
+Injection risks, quoting rules, and strict-mode checks relevant to security.
+
+[§16 Internationalization](https://github.com/toon-format/spec/blob/main/SPEC.md#16-internationalization):
+Unicode handling and locale-independent number formatting.
+
+[§17 Interoperability and Mappings](https://github.com/toon-format/spec/blob/main/SPEC.md#17-interoperability-and-mappings):
+JSON/CSV/YAML mappings and conversion guidance.
+
+[§18 IANA Considerations](https://github.com/toon-format/spec/blob/main/SPEC.md#18-iana-considerations):
+Media type registration plans and provisional status.
+
+[§19 TOON Core Profile](https://github.com/toon-format/spec/blob/main/SPEC.md#19-toon-core-profile-normative-subset):
 Normative subset of the most common, memory-friendly rules. Useful for minimal implementations.
 
-**[Appendix G: Host Type Normalization Examples](https://github.com/toon-format/spec/blob/main/SPEC.md#appendix-g-host-type-normalization-examples-informative)**
+[Appendix G: Host Type Normalization Examples](https://github.com/toon-format/spec/blob/main/SPEC.md#appendix-g-host-type-normalization-examples-informative):
 Non-normative guidance for Go, JavaScript, Python, and Rust implementations on normalizing language-specific types.
 
-**[Appendix C: Test Suite and Compliance](https://github.com/toon-format/spec/blob/main/SPEC.md#appendix-c-test-suite-and-compliance-informative)**
+[Appendix C: Test Suite and Compliance](https://github.com/toon-format/spec/blob/main/SPEC.md#appendix-c-test-suite-and-compliance-informative):
 Reference test suite at [github.com/toon-format/spec/tree/main/tests](https://github.com/toon-format/spec/tree/main/tests) for validating implementations.
 
 ## Spec Sections at a Glance
@@ -89,28 +105,35 @@ Reference test suite at [github.com/toon-format/spec/tree/main/tests](https://gi
 | §7 | Strings, keys, quoting, escaping | Implementing string handling |
 | §8-10 | Objects, arrays, list items | Implementing structure encoding |
 | §11-12 | Delimiters, indentation, whitespace | Implementing formatting and validation |
-| §13 | Conformance, options, key folding | Implementing options and features |
+| §13 | Conformance, options, key folding/path expansion | Implementing options and features |
 | §14 | Strict-mode errors | Implementing validators |
+| §15-18 | Security, i18n, interoperability, media type | Operational and ecosystem considerations |
 | §19 | Core profile | Minimal implementations |
+| §20-21 | Versioning, extensibility, IP | Long-term stability and licensing |
 
 ## Conformance Checklists
 
 The spec includes three conformance checklists:
 
-### [Encoder Checklist (§13.1)](https://github.com/toon-format/spec/blob/main/SPEC.md#131-encoder-conformance-checklist)
+### Encoder Checklist (§13.1) <sup>[↗ SPEC.md](https://github.com/toon-format/spec/blob/main/SPEC.md#131-encoder-conformance-checklist)</sup>
 
 Key requirements:
 - Produce UTF-8 with LF line endings
 - Use consistent indentation (default 2 spaces, no tabs)
-- Escape only `\\`, `\"`, `\n`, `\r`, `\t` in quoted strings
+- Escape only `\\`, `\"`, `\n`, `\r`, `\t` in quoted strings; any other escape is invalid
 - Quote strings with active delimiter, colon, or structural characters
 - Emit array lengths `[N]` matching actual count
 - Preserve object key order
 - Normalize numbers to non-exponential decimal form
 - Convert `-0` to `0`, `NaN`/±Infinity to `null`
 - No trailing spaces or trailing newline
+- When `keyFolding="safe"` is enabled, folding MUST follow §13.4:
+  - Only fold IdentifierSegment keys (letters/digits/underscores, no dots),
+  - Do not introduce collisions with existing sibling keys,
+  - Do not fold segments that would require quoting.
+- When `flattenDepth` is set, folding MUST stop at the configured number of segments (§13.4).
 
-### [Decoder Checklist (§13.2)](https://github.com/toon-format/spec/blob/main/SPEC.md#132-decoder-conformance-checklist)
+### Decoder Checklist (§13.2) <sup>[↗ SPEC.md](https://github.com/toon-format/spec/blob/main/SPEC.md#132-decoder-conformance-checklist)</sup>
 
 Key requirements:
 - Parse array headers per §6 (length, delimiter, fields)
@@ -119,15 +142,21 @@ Key requirements:
 - Type unquoted primitives: true/false/null → booleans/null, numeric → number, else → string
 - Enforce strict-mode rules when `strict=true`
 - Preserve array order and object key order
+- When `expandPaths="safe"` is enabled, expand dotted keys into nested objects per §13.4:
+  - Split on `.`, only expand when all segments are IdentifierSegments,
+  - Deep-merge overlapping paths (object + object),
+  - Do not perform element-wise array merges.
+- With `expandPaths="safe"` and `strict=true` (default), MUST error on any expansion conflict (§14.5).
+- With `expandPaths="safe"` and `strict=false`, MUST apply deterministic last-write-wins (LWW) conflict resolution (§13.4).
 
-### [Validator Checklist (§13.3)](https://github.com/toon-format/spec/blob/main/SPEC.md#133-validator-conformance-checklist)
+### Validator Checklist (§13.3) <sup>[↗ SPEC.md](https://github.com/toon-format/spec/blob/main/SPEC.md#133-validator-conformance-checklist)</sup>
 
 Validators should verify:
 - Structural conformance (headers, indentation, list markers)
 - Whitespace invariants (no trailing spaces/newlines)
 - Delimiter consistency between headers and rows
 - Array length counts match declared `[N]`
-- All strict-mode requirements
+- All strict-mode requirements (including path-expansion conflicts when enabled)
 
 ## Versioning