Syntactic Trees in Forest

Forest Syntactic Trees for Obsidian

Render LaTeX forest-style syntactic trees inline in Obsidian notes. Node labels go through Obsidian's MathJax pipeline, so primes (X$'$), superscripts (X$^0$), subscripts and arbitrary inline math just work.

The plugin focuses on the subset of forest that linguists actually use for syntactic trees: bracket syntax, per-node options, the for tree propagator, edge labels, triangle (roof) phrases, and \draw-style movement arrows between named nodes — with TikZ-faithful to[…] semantics.

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Usage

Trees live in fenced forest code blocks:

```forest
[CP
  [DP, name=who [who]]
  [C$'$
    [C [did]]
    [TP
      [DP [Mary]]
      [T$'$
        [T [see]]
        [VP, name=tr, roof [$t_i$]]]]]]
\draw[->] (who) to[out=south, in=south] (tr);
```

The plugin processes the source as forest-package syntax and emits an inline SVG. Labels are MathJax-rendered, so anything between $…$ typesets properly.

```forest is the sole entry point — $$\begin{forest}…\end{forest}$$ is not supported because MathJax doesn't know the forest environment and would raise an error before the plugin could intervene.

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Bracket syntax

Every node sits in [ … ]. Children are nested directly:

[Parent [Child1] [Child2 [Grandchild]]]

To put a literal [, ], ,, or = into a label, brace-protect that chunk: [{a, b}].

Per-node options

A comma after the node content introduces a comma-separated option list:

[VP, draw, name=verb, tier=word]

Inheritance: for tree and for descendants

Apply options to a node and all its descendants:

[CP, for tree={parent anchor=south, child anchor=north}
  [DP] [C$'$ [C] [TP]]]

for descendants={...} does the same but excludes the node itself.

Line breaks in labels

LaTeX-style \\ inside a node label breaks it into stacked, centered lines:

[NP [Tall] [N\\cat]]

renders the second child as "N" over "cat". \\ inside $…$ math is left alone — there it's MathJax's own row separator (matrices, \begin{array}, etc.), so things like $\begin{matrix}a\\b\end{matrix}$ still typeset correctly. Node width/height and edge anchors adapt to the stacked size automatically.

Math in labels

Anything between $…$ in a node label is rendered with MathJax:

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Sizing trees and nodes

Forest's TeX-dimension size options can sit on any node — root or interior — and apply locally:

X is a TeX dimension: pt, pc, bp, cm, mm, em, ex, in, px, or a bare number (= pixels). 1 pt ≈ 1.333 px, 1 cm ≈ 37.8 px at 96 dpi.

Local overrides on inner nodes only affect that node's children:

[VP                              ← root spacing default
  [DP [Mary]]
  [V$'$, s sep=18pt, l sep=28pt  ← V's subtree breathes out, rest stays tight
    [V [saw]]
    [DP [John]]]]

To apply to a whole subtree, use the propagator:

[CP
  [DP]
  [C$'$
    [C]
    [TP, for tree={l sep=22pt, s sep=14pt}
      [DP] [T$'$ [T] [VP]]]]]

---

Movement arrows

After the tree, you can add \draw commands between nodes:

[CP
  [DP, name=moved [who]]
  [C$'$ [C] [TP [DP [Mary]] [T$'$ [T] [VP [V [saw]] [DP, name=trace [$t_i$]]]]]]
]
\draw[->] (moved) to (trace);
\draw[->, dashed] (a) to[bend left=45] (b);
\draw[->, dotted] (a) to node{move} (b);
\draw[->, solid] (a) -- (b);

Recognised within each \draw:

Direction control: to[out=A, in=B]

Per TikZ semantics, out=A and in=B set both the attachment point on the node boundary AND the tangent direction there. The attachment is the intersection of the ray from the node's centre at angle A with the node's bounding box. So out=south attaches at the south boundary and the curve leaves heading south.

You can use compass names or polar angles (0°=east, 90°=north, 180°=west, 270°=south):

\draw[->] (a) to[out=south,      in=south]      (b);
\draw[->] (a) to[out=south west, in=south]      (b);
\draw[->] (a) to[out=east,       in=west]       (b);
\draw[->] (a) to[out=270,        in=180]        (b);
\draw[->] (a) to[out=south east, in=north west, looseness=1.4] (b);

Compass-name → angle: east=0°, north east=45°, north=90°, north west=135°, west=180°, south west=225°, south=270°, south east=315°.

Whitespace inside compound names is tolerated. An optional looseness=N (default 1) scales how strongly the tangent is enforced — higher values exaggerate the curve.

Bend modifiers

bend left=N and bend right=N rotate the tangent angles. Combined with out/in, they add N° CCW to out and subtract N° from in (for bend left), bowing the curve further to that side of the path direction:

\draw[->] (a) to[out=south, in=east]                 (b);   ← baseline
\draw[->] (a) to[out=south, in=east, bend left=20]   (b);   ← bows more left
\draw[->] (a) to[out=south, in=east, bend right=20]  (b);   ← bows more right

Used alone (without out/in), bend left=N / bend right=N produce a quadratic curve bowing to that side of the direct line.

Anchor shorthand: (name.south)

For simple cases you can also pin an endpoint to a named anchor directly: (name.south), (name.east), (name.north west), etc. This is shorthand that pins the attachment point and uses the corresponding outward tangent direction. The full TikZ list is supported:

north, south, east, west, north east, north west, south east, south west, center.

When you give neither an anchor nor out=/in=, the renderer auto-picks the side of each node facing the other endpoint.

Arrowheads

Drawn geometrically as filled triangles oriented along the curve's tangent at the endpoint — no dependence on SVG <marker> definitions, which makes them robust across themes and embedded-SVG quirks. Style mimics TikZ's default > (slim, slightly concave back).

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Settings

A settings tab exposes the global visual defaults: level separation, sibling separation, subtree separation, label font size, edge stroke width, and a toggle to outline every node by default. Per-tree options (above) override these locally.

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Styling

The default look is aligned with TikzJax-rendered TikZ output (Computer- Modern-style serif text, thin crisp lines, refined arrow tips). Customize further with a CSS snippet targeting any of:

All strokes and fills resolve through currentColor, set from color: var(--text-normal) on the SVG. So one rule recolors everything:

.forest-svg { color: #003366; font-family: "EB Garamond", serif; }

Dark mode is automatic because --text-normal flips with the theme.

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Installation

1. Download main.js, manifest.json, styles.css from the release.
2. Drop them into <your-vault>/.obsidian/plugins/obsidian-forest/.
3. Reload plugins in Obsidian settings, then enable Forest Syntactic Trees.

To build from source:

npm install
npm run build

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What this plugin is not

It is not a complete port of the forest LaTeX package. forest is a TikZ/PGF DSL with conditionals, dynamic trees, aggregate functions, custom handlers, externalization, etc. — none of which is sensible to reimplement in JavaScript. This plugin covers the slice syntacticians reach for daily: bracket trees, primes and bars in labels, triangles, named nodes, movement arrows, and TikZ-style direction control via out=/in= and bend.

Verifying which version is running

Every rendered SVG carries a data-forest-version attribute (visible in dev tools), and the plugin logs [forest] plugin loaded — v<version> on load. If a feature isn't behaving as documented, check these first to confirm the bundle on disk is the one Obsidian actually loaded.

License

MIT.