Model

Without a shared model, every language would repeat validation and every stage would read every language. svugy-model defines the Model all parsers produce and all stages read, and validates it once.

Components

ElementPath is an element’s only identity, in the model and in the SVG.

• Segments from the top down, dot-joined: pipeline.inter; a segment holding ., " or \ is quoted. The root is the empty path.
• Depth = segment count: root 0, top-level element 1.

Model holds the diagram.

• elements: BTreeMap<ElementPath, Element>. An element with children is a container; there is no container flag.
• edges: BTreeMap<EdgeId, Edge>. EdgeId is (from, to, ordinal), shown (a -> b)[0]; the ordinal keeps parallel edges apart.
• A badge edge is drawn as a mini of its target on its source’s top face instead of an arc.
• An edge’s home level, where layout places it, is its endpoints’ lowest common ancestor.
• Fields are crate-private: outside svugy-model, a non-empty Model exists only after admission.

ModelBuilder builds a model through handles.

• add_top_level and add_child return an ElementRef; parents and edge endpoints are ElementRefs, so they exist by construction.
• add_edge assigns the pair’s next free ordinal.
• Markdown and d2 lower through it; Rust programs call it directly (Rust).

Admission (UncheckedModel::admit) rejects unsound models.

• Returns ModelAdmission { model, report }; model is None if any problem is an error. Warnings never block.
• Problem (problem.rs) lists all 17 problem kinds, from dangling references and duplicate paths to unknown styles and badges on containers.
• Every position, height and numeric style is bounded by MAX_MAGNITUDE = 1e6, so no valid model yields a huge SVG.
• Unknown names get “did you mean”: the closest candidate by case-insensitive Levenshtein distance, if ≤ ⌊len / 3⌋.

DisclosedModel cuts the model into the layers the interactive SVG steps through.

• Layers 0 to D, D being the depth of the deepest container. Layer D is the model.
• Layer K keeps elements of depth ≤ K + 1. Containers at depth K + 1 lose their children, becoming leaves; closed_containers lists them.
• An edge with a hidden endpoint moves to that endpoint’s shown ancestor; it is dropped if both ends land on one element.
• Moved edges between one ordered pair merge into one, under the pair’s next free ordinal; lifted_origins lists what it stands for.
• Layout reads a layer as a plain Model; geometry and render also read closed_containers and lifted_origins.

Example: elements a, a.x, a.y, b, edges a.x -> b and a.y -> b. Layer 0 holds a (closed) and b, joined by (a -> b)[0], standing for both edges. Layer 1 is the model.

Code: crates/svugy-model/src/.