---
title: "modelcheck-library-section-fences — Mova code model"
description: "Mova code model of tools/modelcheck/src/sections.rs: components with their labels, obernants and the model text."
url: "https://groupants.elamur.ai/free/en/mova/tools/modelcheck/src/sections.rs.groupant/section-fences.groupant/"
---
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# modelcheck-library-section-fences

The groupant beside tools/modelcheck/src/sections.rs in the Mova repository: what the code computes, what it never does, how to go back from its outputs, its invariants, cost and checks.

## Facts

- **kind:** groupant_fragment
- **status:** partial
- **source:** [`tools/modelcheck/src/sections.rs`](https://github.com/ElamurAI/mova-free/blob/main/tools/modelcheck/src/sections.rs)
- **source SHA-256:** `c05b5d875d6fffdd…`
- **covers:** Narrow H2 fence automaton (bytes 254–3689)
- **part of:** [modelcheck-sections](https://md.groupants.elamur.ai/free/en/mova/tools/modelcheck/src/sections.rs.groupant/)
- **repository folder:** [`tools/modelcheck/src/sections.rs.groupant/section-fences.groupant`](https://github.com/ElamurAI/mova-free/tree/main/tools/modelcheck/src/sections.rs.groupant/section-fences.groupant)
- **repository commit:** `855da7bd4a7b`

> **Implementation material.** A Mova code model describes this code at one source revision: partial models, finite checks and their stated scope. It is not a reviewed general exposition, and its labels are shown as written, never raised.

## Components

| component | label | where |
|---|---|---|
| **approximant** | partial | [Forward](#forward) |
| **ast** | partial | `../syntax.json` |
| **cost** | partial | [Cost](#cost) |
| **descriptant** | partial | [Descriptant](#descriptant) |
| **invariant** | partial | [Invariant](#invariant) |
| **tests** | partial | [Tests](#tests) |

## Obernants

The typed relations around the forward model: the behaviour complement (what the code never does), the reverse reconstruction (every input compatible with an output) and specialised views.

| id | type | label | where |
|---|---|---|---|
| `behavior_complement` | behavior_complement | partial relational specification | [behavior_complement](#behavior-complement) |
| `reverse_reconstruction` | reverse_reconstruction | partial relational specification | [reverse_reconstruction](#reverse-reconstruction) |
| `closing_threshold` | closing_threshold | partial relational specification | [closing_threshold](#closing-threshold) |
| `opening_info_constraint` | opening_info_constraint | partial relational specification | [opening_info_constraint](#opening-info-constraint) |
| `duplicate_count_semantics` | duplicate_count_semantics | partial relational specification | [duplicate_count_semantics](#duplicate-count-semantics) |
| `unterminated_fence_suffix` | unterminated_fence_suffix | partial relational specification | [unterminated_fence_suffix](#unterminated-fence-suffix) |

## Model text


Subject: current manifest source SHA and exact UTF-8 range [254,3689) of sections.rs. The observation is one completed scoped call with adequate resources; source-derived relations are partial specifications. Filesystem checks describe sequential reads, not an atomic snapshot.

### Forward

Scan lines with state Outside or (opening marker,run length). Outside, admit <=3-space backtick/tilde runs >=3 with backtick-info restriction; otherwise count exact column-zero H2 string. Inside, close only same marker at least opening length with whitespace-only suffix and skip every line from counting.

### Invariant

Only exact unfenced H2 lines count. Closing fence lines never count. The scan counts all occurrences so duplicate headings remain detectable; it is not a Markdown renderer.

### Cost

O(B) scanned bytes and O(H) heading-string allocation for B artifact bytes and H section bytes; constant fence state. Each component's section read rescans independently.

### Descriptant

Wave34, 2026-10-31: deeper scope retained under its existing parent without replacing historical views. Decode reuse was proposed before edits and checked against actual reference decoding; behavioral controls and repeated native receipts remain finite evidence. No numerical surrogate is justified for categorical validation outcomes; no percentage accuracy or complete semantic proof is claimed.

### Tests

Exact native test: groupant_tests::groupant_validation_negative_controls_and_open_extensions. Parent tests additionally exercise integration and failure order. Current evidence is in ../../wave34-evidence.md; old evidence remains explicitly historical in wave33-evidence.md at the source root.

### behavior_complement

Exclude positive heading increments for lines inside a recognized fence, padded headings, wrong heading level or heading text with trailing markup. These excluded transitions are defined by current fence state and exact line equality.

Assurance: source-derived partial relation; fixed source revision and stated scope. Oracle: groupant_tests::groupant_validation_negative_controls_and_open_extensions. Finite observations do not establish universal completeness.

### reverse_reconstruction

Observed count k admits all texts whose outside-state exact-heading events number k. Fence contents and unrelated lines remain unconstrained; k=1 cannot recover a unique document.

Assurance: source-derived partial relation; fixed source revision and stated scope. Oracle: groupant_tests::groupant_validation_negative_controls_and_open_extensions. Finite observations do not establish universal completeness.

### closing_threshold

Given state (m,L), a line closes iff indent<=3, marker=m, run>=L and remaining suffix is space/tab only. Short runs or other marker preserve the state.

Assurance: source-derived partial relation; fixed source revision and stated scope. Oracle: groupant_tests::groupant_validation_negative_controls_and_open_extensions. Finite observations do not establish universal completeness.

### opening_info_constraint

Outside-state backticks with another backtick in suffix do not open; tilde suffixes have no equivalent restriction. The distinction is intentional narrow grammar.

Assurance: source-derived partial relation; fixed source revision and stated scope. Oracle: groupant_tests::groupant_validation_negative_controls_and_open_extensions. Finite observations do not establish universal completeness.

### duplicate_count_semantics

A document with two admitted exact headings yields 2; the caller requires count=1 and rejects both missing and ambiguous sections. Early success at first match would weaken validation.

Assurance: source-derived partial relation; fixed source revision and stated scope. Oracle: groupant_tests::groupant_validation_negative_controls_and_open_extensions. Finite observations do not establish universal completeness.

### unterminated_fence_suffix

After an opening without an admissible closer, all later headings are suppressed. Prefixing an opener can therefore change the compatible-document fiber for an unchanged suffix.

Assurance: source-derived partial relation; fixed source revision and stated scope. Oracle: groupant_tests::groupant_validation_negative_controls_and_open_extensions. Finite observations do not establish universal completeness.

### Epoch 2026-11-04

Moved from `lib.rs` (component validation) to `sections.rs`, shared with consolidation. The automaton is now `lines` (per-line fenced flag, delimiter lines included), `unclosed_fence` and `heading_count`; the counted relation is unchanged: exact column-zero `## Name` lines outside fences. New in this range: `h2_names` lists every unfenced line starting with `## `. Additional oracle: `sections::tests::sections_follow_the_plain_h2_grammar` (duplicates and unclosed fences as negative controls).