layout-cat 0.1.0

Box-model layout: cascade + block layout over a dom-cat tree using css-cat stylesheets. Produces a LayoutBox tree with positions and dimensions. No mut, no Rc/Arc, no interior mutability, no panics, exhaustive matches. Fourth sub-crate of a Servo-replacement webview runtime targeting Tauri.
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# layout-cat

Box-model layout engine: cascade CSS rules over a DOM tree and compute a `LayoutBox` tree with positions and dimensions.

`layout-cat` is the fourth sub-crate of a `comp-cat-rs` Servo-replacement webview runtime targeting Tauri integration.  It consumes a [`dom-cat`](https://crates.io/crates/dom-cat) document and a [`css-cat`](https://crates.io/crates/css-cat) stylesheet, applies a simple cascade, and lays out block-level boxes.  Same framework constraints: no `mut`, no `Rc`/`Arc`, no interior mutability, no panics.

## Example

```rust
use layout_cat::{layout, Error, Viewport};

fn main() -> Result<(), Error> {
    let html_doc = html_cat::parse("<html><body><p>hi</p></body></html>")?;
    let dom = dom_cat::Document::from_html_doc(&html_doc);
    let sheet = css_cat::parse("p { width: 100px; padding: 8px; }")?;
    let tree = layout(&dom, &sheet, Viewport::new(800, 600));
    assert!(tree.root_box().is_some());
    Ok(())
}
```

## v0 scope

- Cascade: match `css-cat` rules to `dom-cat` elements (via dom-cat's matcher) and resolve declarations to a `ComputedStyle`.
- Length resolution: px, em (multiplier on `font-size`), percentage (against containing-block width).
- Box model: margin / border / padding / content per element.
- Block layout: vertical stacking with width/height/margin/padding arithmetic.
- `LayoutTree` of `LayoutBox` with positions, dimensions, and a back-reference to the originating `dom_cat::NodeId`.

## Deferred to v0.2+

- Inline layout, text shaping.
- Flex / grid / floats / positioning (other than `static`).
- Real font metrics; v0 uses `16px` as the default font size.
- Tables, transforms, logical properties.

## License

MIT OR Apache-2.0