Text Rendering Features and Hosts

Markdown and feature extensions

Markdown renders Codex-style headings, inline code, links, blockquotes, lists, thematic breaks, fenced code, and GFM tables at natural content width. Layout never depends on the viewport, zoom, or paste position. Disabled inline rules consume delimiters without styling; disabled block rules preserve their source slice. Raw mode preserves all delimiters. Renderer results may be asynchronous, and clipboard commands await them before mutating Canvas. Inputs at or above 50,000 UTF-16 code units render in a module worker. Worker tasks may be cancelled, and a worker failure is surfaced instead of retrying a large render on the main thread. The protocol layout is a streaming grapheme pass; a 10,000-line result stays as row spans until Canvas applies one compact CellPlane operation.

CharGraph owns the browser-safe Markdown core adapted from marked-terminal, Shiki code highlighting, and independent Mermaid and math renderers. Each built-in Markdown module registers its parser extensions, feature identities and color defaults, and semantic style contribution once. The module registry derives the default extension manifest, public feature contracts, and render options; the theme layer only aggregates module contributions. Markdown syntax extensions may contribute marked tokenizers and transform tokens or fenced languages into the same fragment IR. CharGraph's built-in extension manifest registers Alert, Diff, JSON/YAML trees, Mermaid, Cartesian charts, and math once for rendering and detection. The document feature registry binds those engine features to Canvas labels, settings groups, color-row layout, and legacy profile aliases; it does not own parser registration or renderer styles. Unsupported, invalid, or oversized Mermaid input falls back to the complete fenced source with a diagnostic; disabling Mermaid keeps the inner source as an ordinary code block. Neither renderer imports terminal capability detection or Node polyfills. Markdown consumes marked tokens through a character renderer rather than its HTML renderer. Unsupported images and raw HTML preserve their original source with a diagnostic; generated HTML cannot leak into Canvas output.

Host and persistence boundaries

The chardesk CLI is a headless host of the same contracts. CharGraph input becomes styled fragments and Protocol layout; .chardesk input enters at Protocol decode. check stops at that compiled document. render sends it to a plain, ANSI, ESC-less CharDesk, or PNG backend; only PNG creates the shared Rendering model and uses its Canvas painter with vendored fonts on Node Canvas. Node resolves a vendored font shard per grapheme; the CLI isolates the native PNG painter so a backend signal becomes raster-backend-crash. ANSI serialization is an explicit output backend, never an internal step toward PNG. Browser workers, profiles, clipboard commands, and persistence remain application concerns.

Container extensions may call the context's renderBlocks capability to render child marked tokens through the same rules, styles, source mapping, diagnostics, and extension set. GitHub Alerts use marked-alert for tokenization and render NOTE, TIP, IMPORTANT, WARNING, and CAUTION as a colored left rail while preserving nested Markdown. Unified diff and patch fences classify metadata, hunks, added, deleted, and context lines; additions and deletions receive semantic foreground and lightly mixed background colors. Diff does not infer a programming language, compare words, or apply patches.

JSON and YAML tree extensions turn json, jsonc, yaml, and yml fences into the same compact Unicode key tree. JSON uses jsonc-parser offsets; strict JSON and comment-tolerant JSONC remain separate dialects. YAML uses yaml document nodes, preserves document order, anchors, aliases, and merge keys without resolving aliases, and rejects complex mapping keys that the compact grammar cannot represent. The two features have independent switches and semantic color slots. Disabling a tree returns the fence to Shiki; invalid, unsupported, or bounded-out input preserves the complete fenced source with a diagnostic. Tree conversion is limited to fenced Markdown and does not detect bare clipboard data. Connectors, keys, array indices, strings, numbers, booleans, nulls, and empty containers have separate roles; YAML adds a reference role for anchors, aliases, and tags. Keys use color without font emphasis. Previous keyword overrides expand across boolean, null, empty, and YAML reference roles when profiles are decoded.

Math uses Temml's public TeX-to-MathML output and a DOM-free MathML adapter. Inline $…$ and \(…\) become compact Unicode; block $$…$$, \[…\], and math/tex/latex fences become a baseline-aware two-dimensional character box before flattening to fragments. Layout cells preserve MathML semantics through fragment output: identifiers use italic content, numbers and text remain upright, operators use the accent role, and generated fraction, radical, and fence glyphs use the muted structure role. MathML invisible operators U+2061–U+2064 are removed before visible cells are created. Inline and block rules have independent switches and share one Math palette with content, operator, and structure slots. The adapter owns character-cell layout only; it never parses TeX or exposes Temml's private syntax tree. Invalid or bounded-out formulas preserve their complete Markdown source with a diagnostic and the Renderer Theme danger color. Previous inline and block foreground overrides migrate to shared content, preferring inline when both exist.

TextRenderProfile.renderTheme stores optional semantic token overrides; the resolved Renderer Theme is independent from the host UI theme. Profile v2 stores each rule's enabled state and local color overrides under features. CharGraph's Renderer Theme owns the shared token palette; Markdown and Mermaid own their semantic defaults and style factories. Canvas and the CharGraph showcase are separate hosts of those contracts. rendering/features.ts owns settings labels, host grouping, compatibility, and persistence; its public registry derives identity and slot defaults from CharGraph contracts. Display settings and settings search derive from that registry rather than parallel UI maps. Style precedence is explicit ANSI, feature color override, Renderer Theme token, then inherited paste style. Each feature definition owns its slots' token or inheritance defaults. Quote and heading colors belong to their markers; inline code owns foreground and background slots; table headers own foreground and background slots while separators are independent. Fenced-code scopes remain owned by Shiki. CharGraph derives their token colors from the resolved Renderer Theme; the bare library API keeps github-light as its compatibility fallback. Mermaid emits semantic roles for node, edge, label, arrow, container, chart grid, and data series cells; the document registry maps those roles to Renderer Theme tokens and feature-local overrides. Node fill remains transparent by default. Persisted single-foreground Mermaid settings expand across the new foreground roles, while profile v1 rules and global color keys migrate to feature-local profile v2 settings on first read. Like every renderer setting, style changes affect future paste only because Canvas stores materialized cells.