# Spring nodes and two-point paths

Use the same `spring` style in either drawing API. Both forms use TikZ's
coil decoration and share `pre length`, `post length`, `amplitude`,
`segment length`, `aspect`, and the `every spring` hook.

## Connect two attachment points

```latex
\draw[spring,pre length=3mm,post length=5mm]
  (A) -- node[midway,above=3mm] {$k$} (B.west);
```

The endpoints determine the spring's total length and direction. This is
convenient when the two bodies are already positioned. The path has no
private node anchors; name its endpoint coordinates if needed.

## Position a named spring

```latex
\node[spring,minimum width=3cm,rotate=30,anchor=start] (S) at (A) {};
\node[block,anchor=west] (B) at (S.end) {$m$};
```

The default node is horizontal and 3 cm long, centred at its placement
coordinate. `spring length` is a unit-aware alias of `minimum width`;
`rotate` rotates both the coil and its anchors. Use `anchor=start` when
placing it at its first attachment. Native TikZ transformations and styles
work as usual. The collision-safe `physicsspring` and `physics spring`
spellings support both forms too.

| Node anchor | Meaning |
| --- | --- |
| `start`, `end` | Exact axis attachment points, excluding outer separation |
| `center` | Midpoint of the complete spring axis |
| `coil-start`, `coil-end` | Axis positions after the first lead and before the last lead |
| `axis-0..100` | Integer percentages along the full straight axis; 0=start, 50=center, 100=end |
| Compass anchors | Coil envelope, enlarged by `minimum height` and outer separation |

`axis-*` samples the axis, not the helical wire. `minimum height` reserves
space without changing coil amplitude. Both lead lengths may be zero; their
sum must be smaller than the node's length. Amplitude and segment length
must be positive. Set labels above or below the node to keep them off the
coil. Prefer `start` and `end` for physical connections.

## Inspect anchors and keys

```latex
\node[spring,minimum width=4cm,show anchors,show keys,
  physics debug/anchor families={axis},
  physics debug/anchor samples={0,25,50,75,100}] (S) {};
```

The numbered marker table and key card also work on unnamed and rotated
spring nodes. `show keys` lists documented defaults, not the applied node
values. For either API, use `\physicshelp{spring}` inside a `tikzpicture`.
Debug overlays stay off in finished diagrams.

The [four-page visual gallery](spring-node-path.pdf) compares
horizontal, vertical, and inclined paths with nodes, shows both debug
panels, and connects a spring node directly to a wall and block. Its
[copy-ready source](../examples/spring-node-path.tex) compiles with:

```sh
pdflatex -interaction=nonstopmode -halt-on-error -output-directory=output/pdf \
  examples/spring-node-path.tex
```