Pacem JS - <pacem-rescale>

`<pacem-rescale>` is a *behavior* that adds resize handles to any element: split panes, dashboard widgets, crop boxes.
Declare it, attach it through `behaviors`, set the limits.

```html
<pacem-rescale id="resize" handles="right" min-width="160" max-width="480"></pacem-rescale>

<aside behaviors="{{ [#resize] }}">…</aside>
```

## Usage

**Attach it.** One `<pacem-rescale>` serves any number of elements, through their `behaviors`.
`handles` picks the edges (`top`, `right`, `bottom`, `left`, or `all`, the default); corners come with the edges they join.

**Set the limits.** `min-width`, `max-width`, `min-height`, `max-height`, in pixels: a drag beyond them stops at the limit.
`keep-proportions` keeps the width/height ratio (and leaves the corners only).

> Sizes are the element's outer (border-box) sizes, whatever its `box-sizing`: the behavior takes padding and borders
> into account when it writes `width`/`height`, so the limits are the size you see.

**React.** `rescale` fires on every move with the size about to be applied (`detail.targetRect`); `rescalestart` and `rescaleend` frame the gesture.

> `rescale` is cancelable: `preventDefault()` and nothing gets applied, then apply the size your way
> (as a percentage, a grid span, a setting saved for next time).

## Customization

The handles are invisible strips (a quarter of the grid spacing thick) on the edges of a `.pacem-rescalable` element:
only the cursor tells they're there. Each one is a `.pacem-rescale` with its side (`.rescale-right`, `.rescale-bottomright`…),
and the `body` gets `.pacem-rescaling` (plus the side) while one is being dragged.

```css
/* show the corner grip, in the accent color */
.pacem-rescalable > .pacem-rescale.rescale-bottomright { opacity: .5; background-color: var(--pacem-color-accent); }
```

## Examples

### A resizable sidebar
The editor's sidebar: right edge only, between 120 and 320 pixels.

### A crop box, 4:3
`keep-proportions`: the corners resize, the ratio stays; `rescaleend` reports the final crop.