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<div class="hm-demo-row" role="group" aria-label="Text style">
  <button type="button" class="toggle" data-toggle aria-pressed="true"><strong>B</strong> Bold</button>
  <button type="button" class="toggle" data-toggle aria-pressed="false"><em>I</em> Italic</button>
  <button type="button" class="toggle" data-toggle aria-pressed="false" data-size="sm"><span style="text-decoration:underline">U</span></button>
</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="toggle-root" data-dz-region>…</div>

How to use it

Seams

• button root carries data-toggle (gallery: data-toggle)
• aria-pressed is the live state; SSR may set the initial value
• toggle.js flips aria-pressed on click (no round-trip)
• named hidden under [data-field-widget=toggle] syncs to aria-pressed

Do / Don't

Pitfalls

• do not use toggle for form booleans — use switch/checkbox
• do not invent exclusive group logic here — use toggle-group radios
• skip disabled / aria-disabled buttons and data-widget bridges

Keyboard / AT

• aria-pressed announces the mode to AT
• Space/Enter activate the button (native button semantics)

Related parts

toggle-group button toolbar

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/toggle.py

Required in the DOM: root [data-toggle] (part toggle). 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: toggle — pressable mode control (toolbar style).

Dual-lock unit is the toggle button root. Label content and size modifiers
are host-owned. Selector ``[data-dz-toggle]`` is the stable substrate root
(gallery CSS; state is ``aria-pressed``).

Emitter: ``widget=toggle`` → ToggleField / free Toggle fragment
(``button.dz-toggle[data-dz-toggle]`` + aria-pressed; ``dz-toggle.js``).
Form hosts may wrap a named hidden carrier in ``[data-dz-field-widget=toggle]``;
the controller syncs that carrier to ``aria-pressed`` on click.
"""

from contracts._kit import DomContract, Node, Present

DOM_CONTRACT = DomContract(
    part="toggle",
    root="[data-dz-toggle]",
    nodes=(
        Node(
            "[data-dz-toggle]",
            attrs={"data-dz-toggle": Present()},
        ),
    ),
)

__all__ = ["DOM_CONTRACT"]

Notes

Source files

One logical Hyperpart, 4 code items (CSS layered, JS bundled). Bound by HYPERPART: toggle — python tools/hyperpart.py toggle lists them.

site/registry.py · contracts/toggle.py · components/toggle.css:1 · controllers/dz-toggle.js