Accessibility reference

This page is the technical contract for Fission accessibility support.

Fission's shared runtime lowers accessibility information into Op::Semantics nodes in Core IR. Shells and renderers consume those semantics differently depending on the target.

Current support matrix

Target	Runtime path	Native accessibility API exposure	Screen-reader expectation	Status
macOS	winit native shell	Yes, through AccessKit and the macOS accessibility stack	VoiceOver, Switch Control, Accessibility Inspector	Supported; product apps still need manual QA.
Windows	winit native shell	Yes, through AccessKit and the Windows accessibility stack	Narrator, NVDA, JAWS, Inspect	Supported; validate on target Windows versions.
Linux	winit native shell	Yes, through AccessKit and AT-SPI where available	Orca and AT-SPI tooling	Supported with desktop/session dependency; validate on the distribution and desktop environment you ship for.
iOS	winit mobile/native shell	Yes, through AccessKit's iOS adapter	VoiceOver, Switch Control, Full Keyboard Access	Supported by the native bridge; validate on simulator and device.
Android	winit mobile shell using NativeActivity	No native TalkBack bridge today	TalkBack, Switch Access, Voice Access	Semantics exist for runtime/tests, but native TalkBack control is not complete because the current AccessKit Android adapter expects winit GameActivity.
Web canvas	winit/Web canvas shell	No DOM accessibility tree for the canvas-rendered app today	Browser screen readers only see surrounding host DOM	Not complete for screen-reader control of the canvas app. Prefer Static site or SSR for accessible document-like pages today.
Static site	static HTML renderer	Yes, through semantic HTML and browser accessibility tree	Browser screen readers and browser accessibility inspectors	Supported for rendered HTML semantics, native form controls, links, headings, labels, and ARIA/data attributes produced by the static renderer.
SSR	server HTML renderer	Yes, through semantic HTML and browser accessibility tree	Browser screen readers and browser accessibility inspectors	Supported for server-rendered HTML semantics and forms, with progressive enhancement preserving semantic targets.
Terminal	terminal shell	No OS accessibility tree owned by Fission	Terminal emulator plus screen reader, for example VoiceOver terminal navigation or Orca terminal use	Partial; Fission semantics inform rendering and tests, but full selector command semantics are not exposed by the terminal backend yet.

Native bridge implementation

The winit shell owns the native accessibility bridge. It uses AccessKit on non-Web, non-Android targets.

The bridge builds an AccessKit TreeUpdate from:

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CoreIR, especially Op::Semantics and text paint operations;

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the latest LayoutSnapshot for bounds and viewport size;

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RuntimeState for focus, text editing state, scroll offsets, and current values.

The root AccessKit node is a window node. Fission semantics nodes become child nodes when they carry meaningful metadata: a non-generic role, label, identifier, value, focusability, checked state, numeric value, scrollability, or actions.

Text paint nodes become read-only labels when they are not already represented by a higher-level semantics node.

Role mapping

Fission role	AccessKit/native role
Role::Button	Button
Role::Text	Label
Role::TextInput	Text input, password input, multiline text input, email input, number input, phone input, or URL input depending on text-input metadata
Role::Image	Image
Role::Checkbox	Checkbox
Role::Radio	Radio button
Role::Switch	Switch
Role::Dialog	Dialog
Role::Slider	Slider
Role::Input	Text input
Role::List	List
Role::ListItem	List item
Role::Generic	Generic container, only emitted when other metadata makes the node meaningful

Static site and SSR targets map some roles to native HTML elements instead: button, input, textarea, input type="checkbox", input type="radio", input type="range", a, ul, li, figure, headings, tables, forms, and labelled wrappers where appropriate.

Exported node data

Fission field or derived data	Native bridge behavior
Semantics::identifier	Exposed as AccessKit author id and as data-fission-semantics in HTML renderers. Used by LiveTest selectors.
Semantics::label	Exposed as accessible label. If absent, some controls derive a label from descendant text.
Semantics::value	Exposed as node value. Text inputs can fall back to retained runtime text-edit state when lowered semantics do not carry a value.
Semantics::focusable	Adds focus and blur actions when the node is enabled.
Runtime focused node	Mirrored into the AccessKit tree focus field.
Semantics::disabled	Exposed as disabled; native action dispatch rejects disabled targets.
Semantics::read_only	Exposed for text inputs and native HTML inputs.
Semantics::checked	Exposed as toggled/checked state for checkbox, radio, and switch controls.
Semantics::masked	Maps text input to password input. The platform accessibility stack decides how to present the value; app code should not place raw secrets in custom semantic values.
Semantics::multiline and text_input_type	Selects multiline, email, number, phone, URL, password, or generic text input role/type.
Semantics::text_selection	Exposed as AccessKit text selection using character indices derived from byte offsets.
Semantics::min_value, max_value, current_value	Exposed as numeric range metadata and supports increment, decrement, and set value.
Semantics::scrollable_x, scrollable_y	Exposes scroll actions and current scroll offsets where layout has scroll geometry.
Action entries	Default, focus, blur, change, cursor change, and related action triggers connect platform actions back to Fission reducers.

Supported native actions

Platform accessibility action	Fission behavior
Click	Dispatches the semantic node's default action if present and enabled.
Focus	Sets Fission runtime focus and dispatches the focus trigger.
Blur	Clears or moves Fission runtime focus and dispatches the blur trigger.
Replace selected text	Focuses the text input and commits replacement text through the IME/text-edit pipeline.
Set value	Updates text input text or numeric range value, then dispatches the relevant change action.
Set text selection	Converts character indices to byte offsets, updates Fission text selection, and dispatches cursor change.
Scroll up/down/left/right	Finds the relevant scroll node, updates runtime scroll offset, and schedules a new frame.
Increment/decrement	Adjusts numeric range values for sliders and similar controls.

Unsupported AccessKit actions are ignored by the bridge today. Add a Fission issue when a product needs a specific missing platform action.

Compatible assistive technology targets

The compatibility target is the operating-system accessibility API, not one named screen reader. Still, product release testing should include common tools.

Platform	Tools worth testing
macOS	VoiceOver, Switch Control, Accessibility Inspector, Keyboard navigation.
Windows	Narrator, NVDA, JAWS, Windows Magnifier, Inspect.
Linux	Orca, AT-SPI inspection tools, high-contrast desktop themes, keyboard-only navigation.
iOS	VoiceOver, Switch Control, Dynamic Type, Full Keyboard Access.
Android	TalkBack, Switch Access, Voice Access, large font scale. Native TalkBack control is not complete yet.
Browser for Static site/SSR	VoiceOver with Safari, VoiceOver with Chrome, NVDA with Firefox/Chrome, JAWS with Chrome/Edge, browser accessibility tree inspectors.

Compatibility still depends on app quality. A supported bridge cannot invent a useful label for an unlabeled icon button, cannot make a color-only error understandable, and cannot choose the right focus order for an ambiguous layout.

Known gaps

Gap	Impact	Current workaround
Android native TalkBack bridge	Android users cannot rely on a complete native screen-reader tree from Fission apps yet.	Keep semantics correct, test with LiveTest, and track Android accessibility bridge work separately.
Web canvas accessibility tree	Browser screen readers cannot inspect the canvas-rendered app as native DOM controls.	Use Static site or SSR for document-like accessible experiences where possible.
Advanced native announcements	Apps may need explicit status announcements for async completion, validation errors, or live regions.	Render visible and semantic status text; add a platform announcement API when needed.
Rich text navigation	Basic text labels and editable selection are exposed, but advanced rich text navigation is not complete.	Keep important prose in normal Text/RichText nodes and validate with target screen readers.
Custom rotors/landmarks	Platform-specific navigation affordances beyond current roles are not fully modeled.	Use clear region labels and roles today; propose additional semantic roles when product needs prove them.
Terminal semantic command tree	Terminal backend does not expose the same selector command semantics as winit LiveTest today.	Use terminal-focused tests and manual terminal/screen-reader QA.