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

The groupant beside tools/modelcheck/src/syntax.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/syntax.rs`](https://github.com/ElamurAI/mova-free/blob/main/tools/modelcheck/src/syntax.rs)
- **source SHA-256:** `35c315cc9b581bea…`
- **covers:** BOM-aware Unicode scalar coordinate table and selected AST preorder visitor (bytes 2943–9398)
- **part of:** [modelcheck-syntax](https://md.groupants.elamur.ai/free/en/mova/tools/modelcheck/src/syntax.rs.groupant/)
- **repository folder:** [`tools/modelcheck/src/syntax.rs.groupant/coordinates-traversal.groupant`](https://github.com/ElamurAI/mova-free/tree/main/tools/modelcheck/src/syntax.rs.groupant/coordinates-traversal.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 | [invariant-and-cost](#invariant-and-cost) |
| **descriptant** | present | [descriptant](#descriptant) |
| **invariant** | partial | [invariant-and-cost](#invariant-and-cost) |
| **tests** | finite native evidence | [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) |
| `bom_offset_translation` | bom_offset_translation | partial relational specification | [bom_offset_translation](#bom-offset-translation) |
| `scalar_boundary_table` | scalar_boundary_table | partial relational specification | [scalar_boundary_table](#scalar-boundary-table) |
| `preorder_stack_induction` | preorder_stack_induction | partial relational specification | [preorder_stack_induction](#preorder-stack-induction) |
| `opacity_projection_fiber` | opacity_projection_fiber | partial relational specification | [opacity_projection_fiber](#opacity-projection-fiber) |

## Model text


### descriptant

#### BOM-aware Unicode scalar coordinate table and selected AST preorder visitor groupant

Epoch 2026-10-31: materialized a scoped view after full-source review. Build per-line scalar boundary byte offsets, shifting base by three for leading BOM. enter converts Span endpoints, checks containment, appends sequential node ID and pushes; visitors recursively visit selected syn fields then pop. Macros enter/leave without body traversal; attributes are skipped.

Root covers original bytes; parent precedes child and contains child interval. Scalar columns are not bytes or grapheme columns. Invalid lookup sets invalid_span and parse later fails; node construction may continue internally.

Useful prior epochs remain in the parent descriptant. This child uses exact byte anchors and the same whole-source hash: editing unrelated bytes also invalidates its binding. The fragment is a partial structural/behavior model, not a proof. No executable percentage surrogate is supplied: categorical gates have no defined useful loss metric; any future profile must use supported caps 1, 2, 5 or 10 percent with explicit domain and evidence.

### catalog

Wave33 historical scope and evidence follow. Current source hashes and refreshed ranges are in manifest.json; wave34 refinements and evidence are at the source root.

## BOM-aware Unicode scalar coordinate table and selected AST preorder visitor typed models

Subject/revision: source SHA-256 in manifest; scope [2943 , 9398). Domain is one completed scoped call on a fixed snapshot with adequate resources, unless narrowed below. Observation includes return/error and declared filesystem effects. Models are source-derived partial relational constraints; complements are inner exclusion hypotheses, converse relations retain compatible-input ambiguity. No universal proof or inverse executor is claimed. Evidence: syntax::tests::nested_projection_is_deterministic_and_source_bound; syntax::tests::unicode_crlf_spans_are_exact_byte_ranges; syntax::tests::bom_and_shebang_keep_original_source_offsets; syntax::tests::macros_are_opaque_and_invalid_rust_fails; syntax::tests::omitted_attributes_macro_bodies_and_external_modules_preserve_shape. Mutation evidence and limits are recorded in ../wave33-evidence.md.

### behavior_complement

Exclude returned nodes with self/later parent, split-codepoint endpoints or parent escape; exclude interpreting macro body tokens or attribute arguments as projected expression children.

Oracle: syntax::tests::nested_projection_is_deterministic_and_source_bound; syntax::tests::unicode_crlf_spans_are_exact_byte_ranges; syntax::tests::bom_and_shebang_keep_original_source_offsets; syntax::tests::macros_are_opaque_and_invalid_rust_fails; syntax::tests::omitted_attributes_macro_bodies_and_external_modules_preserve_shape. Fixed source scope and the stated domain are required; finite checks do not establish untested generality.

### reverse_reconstruction

For fixed source, line/scalar coordinates map to unique stored byte boundaries; without source, node intervals/triples admit many syntax trees and omitted fields. Digest observation constrains but does not prove unique reconstruction.

Oracle: syntax::tests::nested_projection_is_deterministic_and_source_bound; syntax::tests::unicode_crlf_spans_are_exact_byte_ranges; syntax::tests::bom_and_shebang_keep_original_source_offsets; syntax::tests::macros_are_opaque_and_invalid_rust_fails; syntax::tests::omitted_attributes_macro_bodies_and_external_modules_preserve_shape. Fixed source scope and the stated domain are required; finite checks do not establish untested generality.

### bom_offset_translation

A stripped leading BOM contributes base=3 to parser span offsets while root [0,B) and hash use original bytes. No-BOM base=0; BOM+shebang+CRLF is separately exercised.

Oracle: syntax::tests::nested_projection_is_deterministic_and_source_bound; syntax::tests::unicode_crlf_spans_are_exact_byte_ranges; syntax::tests::bom_and_shebang_keep_original_source_offsets; syntax::tests::macros_are_opaque_and_invalid_rust_fails; syntax::tests::omitted_attributes_macro_bodies_and_external_modules_preserve_shape. Fixed source scope and the stated domain are required; finite checks do not establish untested generality.

### scalar_boundary_table

On LF start a new line at offset+1; otherwise append offset+len_utf8(ch). CR is a scalar on CRLF lines. Stored offsets are Unicode scalar boundaries, not grapheme cluster positions.

Oracle: syntax::tests::nested_projection_is_deterministic_and_source_bound; syntax::tests::unicode_crlf_spans_are_exact_byte_ranges; syntax::tests::bom_and_shebang_keep_original_source_offsets; syntax::tests::macros_are_opaque_and_invalid_rust_fails; syntax::tests::omitted_attributes_macro_bodies_and_external_modules_preserve_shape. Fixed source scope and the stated domain are required; finite checks do not establish untested generality.

### preorder_stack_induction

enter assigns id=nodes.len and parent=stack.last, pushes id; corresponding leave pops after descendants. Parent-before-child follows stack discipline but selected syntax omits intermediate AST fields.

Oracle: syntax::tests::nested_projection_is_deterministic_and_source_bound; syntax::tests::unicode_crlf_spans_are_exact_byte_ranges; syntax::tests::bom_and_shebang_keep_original_source_offsets; syntax::tests::macros_are_opaque_and_invalid_rust_fails; syntax::tests::omitted_attributes_macro_bodies_and_external_modules_preserve_shape. Fixed source scope and the stated domain are required; finite checks do not establish untested generality.

### opacity_projection_fiber

Macro/Verbatim/Unknown nodes mark opaque. Changing well-delimited macro tokens leaves selected structural triples compatible; omitted attributes can change bytes and offsets without changing those triples.

Oracle: syntax::tests::nested_projection_is_deterministic_and_source_bound; syntax::tests::unicode_crlf_spans_are_exact_byte_ranges; syntax::tests::bom_and_shebang_keep_original_source_offsets; syntax::tests::macros_are_opaque_and_invalid_rust_fails; syntax::tests::omitted_attributes_macro_bodies_and_external_modules_preserve_shape. Fixed source scope and the stated domain are required; finite checks do not establish untested generality.

### tests

#### Native correspondence

Exact named checks: syntax::tests::nested_projection_is_deterministic_and_source_bound; syntax::tests::unicode_crlf_spans_are_exact_byte_ranges; syntax::tests::bom_and_shebang_keep_original_source_offsets; syntax::tests::macros_are_opaque_and_invalid_rust_fails; syntax::tests::omitted_attributes_macro_bodies_and_external_modules_preserve_shape.

See ../wave33-evidence.md for current repeated profiles, actual production mutants and scope limits. AST generation alone is not behavioral evidence. Each reference test body was read before execution.

### forward

#### Scoped forward model

BOM-aware Unicode scalar coordinate table and selected AST preorder visitor

Build per-line scalar boundary byte offsets, shifting base by three for leading BOM. enter converts Span endpoints, checks containment, appends sequential node ID and pushes; visitors recursively visit selected syn fields then pop. Macros enter/leave without body traversal; attributes are skipped.

### invariant-and-cost

#### Invariant and cost

Root covers original bytes; parent precedes child and contains child interval. Scalar columns are not bytes or grapheme columns. Invalid lookup sets invalid_span and parse later fails; node construction may continue internally.

Boundary table O(B) byte-equivalent storage, selected nodes O(N), stack O(D). enter offsets O(1); visitor O(N plus unprojected visited syn fields). Parsing/recursive stack exhaustion is outside finite test evidence.