Aspect ratio

Copy this

<div class="hm-demo-row" style="gap: var(--space-md); align-items: flex-start;">
  <div class="aspect-ratio" data-ratio="1/1" style="width: 6rem;" aria-label="1:1 frame"><span style="display:grid;place-items:center;background:var(--colour-brand-soft);color:var(--colour-brand-text);font-size:var(--text-xs);">1:1</span></div>
  <div class="aspect-ratio" data-ratio="16/9" style="width: 10rem;" aria-label="16:9 frame"><span style="display:grid;place-items:center;background:var(--colour-brand-soft);color:var(--colour-brand-text);font-size:var(--text-xs);">16:9</span></div>
  <div class="aspect-ratio" data-ratio="4/3" style="width: 8rem;" aria-label="4:3 frame"><span style="display:grid;place-items:center;background:var(--colour-brand-soft);color:var(--colour-brand-text);font-size:var(--text-xs);">4:3</span></div>
</div>

Server exchange

This Hyperpart has no server exchange — it is presentation or client chrome only. htmx does not issue a request on this part's behalf. If you put an affordance (hx-*) on a control that uses this markup, that action's exchange belongs to the action, not this part. See Swap contract for host-owned envelopes.

Swap contract

Agent-visible HTMX topology (ADR-0054 / decision 0012). exchange envelope = what the response may re-emit relative to the persistent slot (body_only | outer | none | host_owned | document). dual-lock validates part markup only — not this envelope. Stem: stems/morph-safe-hypermedia.md; decision: docs/decisions/0012-swap-identity-contract.md.

No host HTMX exchange on this part — presentation or client chrome only. exchange envelope: n/a.

If a host wraps this markup in hx-*, that host owns the swap contract (sole identity + envelope). Prefer innerMorph / outerMorph for stable slots; replacement for flash; body-only responses under inner swaps.

Envelope response examples

This part has no owned exchange (envelope n/a). If a host adds hx-*, that host’s envelope applies — typically body_only:

<!-- Host wraps this presentation part with hx-* (host owns envelope) -->
<!-- Prefer: hx-swap="innerMorph" hx-target="#panel-body" -->
<!-- Server returns body_only interior for #panel-body -->
<div class="dz-stack">content…</div>

Do not re-own the slot:

<!-- WRONG: server returns the presentation root with a new id every poll -->
<div id="aspect-ratio-root" data-dz-region>…</div>

How to use it

No extended guidance authored yet — start from Copy this and the dependency chips (Primitive = markup only; controller = load listed JS; Endpoint = implement Server exchange).

Seams

• copy the partial under Copy this; keep root class and data-* modifiers so the CSS/JS bundle matches
• no Server exchange on this part — pure presentation or client chrome
• satisfy the DOM contract tables (CI stop-ship)

DOM contract

What the emitted HTML must satisfy — the table is the required surface; Python under contracts/ is the package-internal dual-lock CI runs (tests/test_contracts.py), not an app route. Standalone HTMX4: implement the API so responses match this markup. Dazzle: the agent emits SSR that already satisfies it. Do not invent attrs outside these tables. For request/response wiring see Server exchange.

contracts/aspect_ratio.py

Required in the DOM: root .aspect-ratio (part aspect-ratio). Emit only these attributes — inventing extras is fine only if controllers ignore them; omitting required ones fails CI (tests/test_contracts.py).

Module source

Import path is monorepo/package-local (from contracts._kit import …). Source-token form often uses data-*; gallery demos above are unprefixed. Do not copy this into app routes.

"""HYPERPART: aspect-ratio — media frame that locks width/height.

Dual-lock unit is the frame root. ``data-dz-ratio`` presets and child
fill (object-fit) are host-owned. Class ``.dz-aspect-ratio`` is the stable
substrate root — FragmentRenderer ``AspectRatio`` + media-thumb field compose.
"""

from contracts._kit import DomContract, Node

DOM_CONTRACT = DomContract(
    part="aspect-ratio",
    root=".dz-aspect-ratio",
    nodes=(Node(".dz-aspect-ratio", attrs={}),),
)

__all__ = ["DOM_CONTRACT"]

Notes

Source files

Canonical registration in the registry. No dedicated controller — CSS for this part lives in the layered bundle.

site/registry.py · contracts/aspect_ratio.py