Platform Details

xa11y normalizes platform-specific APIs into a unified interface. This page documents how roles and actions map across platforms, and where behavior differs.

Role mapping

xa11y Role	macOS (AX)	Linux (AT-SPI)	Windows (UIA)
Window	AXWindow, AXDrawer	window, frame	WindowControlType
Application	AXApplication	application	(root element)
Button	AXButton	push button	ButtonControlType
CheckBox	AXCheckBox	check box, check menu item	CheckBoxControlType
RadioButton	AXRadioButton	radio button, radio menu item	RadioButtonControlType
TextField	AXTextField, AXSecureTextField	entry, password text	EditControlType
TextArea	AXTextArea	text	EditControlType
StaticText	AXStaticText	label, static, caption	TextControlType
ComboBox	AXComboBox, AXPopUpButton	combo box	ComboBoxControlType
List	AXList, AXOutline	list, list box	ListControlType, TreeControlType
ListItem	(via AXRow)	list item	ListItemControlType
Menu	AXMenu	menu	MenuControlType
MenuItem	AXMenuItem, AXMenuBarItem	menu item, tearoff menu item	MenuItemControlType
MenuBar	AXMenuBar, AXMenuBarExtra	menu bar	MenuBarControlType
Tab	(subrole AXTabButton)	page tab	TabItemControlType
TabGroup	AXTabGroup	page tab list	TabControlType
Table	AXTable	table, tree table	TableControlType, DataGridControlType
TableRow	(via AXRow)	table row	DataItemControlType (no cell signal)
TableCell	AXCell	table cell, column/row header	HeaderItemControlType, DataItemControlType (with TableItem pattern, or parent DataItem)
Toolbar	AXToolbar	tool bar	ToolBarControlType
ScrollBar	AXScrollBar	scroll bar	ScrollBarControlType
Slider	AXSlider	slider	SliderControlType
Image	AXImage	image, icon	ImageControlType
Link	AXLink	link	HyperlinkControlType
Group	AXGroup, AXScrollArea, AXRadioGroup	panel, section, form, scroll pane	GroupControlType, PaneControlType
Dialog	AXSheet (or subrole AXDialog)	dialog, file chooser	WindowControlType (with IsDialog)
Alert	(subrole AXApplicationAlert)	alert, notification	(alert pattern)
ProgressBar	AXProgressIndicator, AXBusyIndicator	progress bar	ProgressBarControlType
TreeItem	AXDisclosureTriangle (or subrole AXOutlineRow)	tree item	TreeItemControlType
WebArea	AXWebArea	document web, document frame	DocumentControlType
Heading	AXHeading (or subrole)	heading	(landmark pattern)
Separator	AXSplitter	separator	SeparatorControlType
SplitGroup	AXSplitGroup	split pane	PaneControlType
Switch	(subrole AXSwitch)	(inferred)	(inferred)
SpinButton	AXIncrementor	spin button	SpinnerControlType
Tooltip	AXToolTip	tooltip, tool tip	ToolTipControlType
Status	AXStatusBar	status bar	StatusBarControlType
Navigation	(landmark)	landmark, navigation	(landmark)

Roles not recognized by a platform map to Unknown.

Action mapping

xa11y Action	macOS	Linux (AT-SPI)	Windows (UIA)
Press	AXPress	click, activate, press, invoke	InvokePattern
Focus	set AXFocused=true	Component.GrabFocus	SetFocus
Blur	set AXFocused=false	(not directly supported)	(not directly supported)
Toggle	AXPress (on checkbox)	toggle, check, uncheck	TogglePattern
Expand	AXShowMenu / AXPress	expand, open	ExpandCollapsePattern.Expand
Collapse	AXCancel / AXPress	collapse, close	ExpandCollapsePattern.Collapse
Select	AXPress	select	SelectionItemPattern
SetValue	set AXValue attribute	Value.SetCurrentValue (numeric) / EditableText.ReplaceText (text)	RangeValuePattern / ValuePattern
TypeText	set AXSelectedText	EditableText.InsertText	ValuePattern (splice)
SetTextSelection	set AXSelectedTextRange	Text.SetSelection	TextPattern range ops
Increment	AXIncrement	increment (or Value +step)	RangeValuePattern (+step)
Decrement	AXDecrement	decrement (or Value -step)	RangeValuePattern (-step)
ShowMenu	AXShowMenu	menu, showmenu, popup	ExpandCollapsePattern
ScrollIntoView	(no-op, no AX equivalent)	Component.ScrollTo	ScrollItemPattern

Platform caveats

ScrollIntoView

macOS has no direct equivalent, so this action is a no-op. On Linux it uses Component.ScrollTo with top-edge alignment. On Windows it uses ScrollItemPattern.ScrollIntoView.

SetValue: text vs numeric

• macOS sets the AXValue attribute directly, which works for both text and numeric values.
• Linux has a Value D-Bus interface that only supports f64, so text values require EditableText.ReplaceText. If neither interface is available, the call returns TextValueNotSupported.
• Windows tries RangeValuePattern for numeric values and falls back to ValuePattern.SetValue for text.

TypeText

Text is inserted through the accessibility API. Keyboard events are never simulated.

• macOS sets AXSelectedText, replacing the selection or inserting at the cursor.
• Linux calls EditableText.InsertText at the current caret offset.
• Windows reads the current value via ValuePattern. It then splices in the new text and calls SetValue.

Blur

• macOS sets AXFocused to false on the element.
• Linux and Windows have no direct API equivalent, so the action is unsupported.

Coordinates

All platforms report bounds as logical (device-independent) screen coordinates with origin at the top-left of the primary display, and Screenshot.scale carries the physical-to-logical ratio for mapping bounds onto captured pixels. Note:

• macOS reports in points, its native logical unit. On Retina displays, 1 point = 2 physical pixels.
• Windows reports device-independent pixels (DIPs), and scale is the display’s DPI scaling (e.g. 1.5 at 150%).
• Linux reports logical pixels where the HiDPI scale is reliably detectable, and falls back to physical at scale 1.0 otherwise. See Coordinates and HiDPI for exactly when.
• Multi-monitor setups can produce negative coordinates for displays positioned left of or above the primary.

Name resolution

Platforms use different attributes to determine an element’s name:

• macOS uses AXTitle, then AXDescription, then AXValue (for text elements).
• Linux uses Accessible.Name, then Description. For StaticText with no name, the first portion of the value is used.
• Windows uses the CurrentName property.

Checked state

The tri-state checked value (Off / On / Mixed) is derived differently:

• macOS parses the AXValue attribute, where "0" = Off, "1" = On, "2" = Mixed.
• Linux uses the AT-SPI state bits Checked (0x10) and Mixed (0x2000).
• Windows reads TogglePattern.CurrentToggleState, where 0 = Off, 1 = On, 2 = Indeterminate.

Selected state

Per-item selection (selected on rows, cells, list items) is read differently:

• macOS uses the per-element AXSelected attribute when present. Some bridges (Qt’s among them) provide no per-element AXSelected and expose selection only through the container’s AXSelectedChildren. For table_cell / table_row / list_item elements whose AXSelected attribute is absent, xa11y resolves selected by membership in the nearest ancestor’s AXSelectedChildren (at most two hops: cell → row → table). Derived values appear in states.selected alone, and raw never gains a synthetic AXSelected key.
• Linux uses the AT-SPI Selected state bit.
• Windows uses SelectionItemPattern.CurrentIsSelected.

Table headers

Header exposure varies by toolkit as well as platform. Windows surfaces header cells as HeaderItem elements and per-cell header relationships via the TableItem pattern. AT-SPI exposes column header / row header roles. AppKit tables expose a header group whose sort buttons carry the column titles. One known toolkit gap: Qt tables on macOS expose no header objects at all. Qt’s Cocoa bridge synthesizes AXRow/AXColumn children only and provides no AXHeader attribute, so column titles are absent from the AX tree and xa11y cannot surface them. This is an upstream Qt limitation. Use the platform-consistent table table_cell selectors for data, and avoid depending on header names for Qt apps on macOS.

Linux: X11 vs Wayland

xa11y supports both X11 and Wayland Linux sessions. Backends are selected at runtime, with no compile-time feature flag.

Capability	X11	Wayland
Accessibility (AT-SPI2)	D-Bus, no display-server dependency	D-Bus, no display-server dependency
Input simulation	XTest extension (no setup)	/dev/uinput virtual evdev device (requires input group)
Screen capture	GetImage on the root window	PNG URI from org.freedesktop.portal.Screenshot

The selection rule:

• DISPLAY set → X11 (regardless of WAYLAND_DISPLAY).
• Otherwise → Wayland: uinput for input, screenshot portal for capture.
• Screenshot also returns Unsupported if neither DISPLAY nor WAYLAND_DISPLAY is set.

Why uinput instead of libei + portal RemoteDesktop?

org.freedesktop.portal.RemoteDesktop (libei) is the architecturally “correct” Wayland input-sim path and the future of structured input injection on Linux, but today it covers a strict subset of the ecosystem: only xdg-desktop-portal-gnome and xdg-desktop-portal-kde support it, and neither has a usable headless mode without a session manager (GDM / SDDM). uinput goes through the kernel and is compositor-agnostic, so it works on every Wayland desktop (GNOME, KDE Plasma, sway, Hyprland, Cosmic, weston) and on headless Linux servers, with the same code path. It is the same mechanism xdotool --using-uinput, ydotool, wtype, Steam Input, and Wine all use.

The trade-off is that uinput requires the user to be in the input group, which grants global input read/write, comparable to macOS Input Monitoring. The portal model is finer-grained (per-app consent) but isn’t broadly available yet. xa11y may add a libei backend later as an opt-in upgrade once the portal landscape stabilises.

Wayland screenshot portal consent

The Screenshot portal usually auto-approves for non-interactive callers (interactive=false, modal=false); xa11y passes both. wlroots compositors via xdg-desktop-portal-wlr and GNOME via xdg-desktop-portal-gnome both support this.

Coordinates and HiDPI

Element.bounds and input Points are logical (device-independent) coordinates, matching the cross-platform contract, and Screenshot.scale reports the physical-to-logical ratio. The scale is detected best-effort and is exact where it can be read reliably:

• Pure X11, integer scaling. Read from Xft.dpi in the X RESOURCE_MANAGER (the same signal GTK/Qt use). AT-SPI extents and XTest are physical, so bounds are divided and input points multiplied by it.
• Single-output Wayland, integer or fractional. The exact ratio physical_mode / logical_size from xdg-output (e.g. 1920 / 1280 = 1.5), rather than the rounded wl_output.scale.

Every other configuration fails closed to 1.0, so the data is never wrong. There, bounds stay physical and the scale is not upscaled, but capture and input round-trips remain correct because bounds and pixels stay in the same space:

• Fractional X11. GTK’s X11 window scale is integer-only, so a fractional Xft.dpi scales fonts, not the coordinate space.
• Multi-monitor mixed-DPI Wayland. A single scalar can’t represent per-monitor scales, so it falls back to the largest integer wl_output.scale (the Windows backend has the same limitation).
• XWayland (both DISPLAY and WAYLAND_DISPLAY set) runs capture through the X11 backend, so the reported scale follows the X11 source and stays 1.0, consistent with that backend.

Point arguments to input simulation, after the logical→physical conversion, are mapped onto the uinput virtual coordinate range. Override the assumed screen size (default 1920×1080) with XA11Y_SCREEN_WIDTH / XA11Y_SCREEN_HEIGHT env vars if your setup differs.

GTK press fallback (Linux)

GTK 4 menu-button widgets (GtkMenuButton, AdwMenuButton, AdwSplitButton) present as an outer push button accessible that advertises NActions = 0 wrapping an inner toggle button that carries the real click action. Calling press() on the outer would normally raise ActionNotSupported. When the owning application identifies itself as GTK via Application.ToolkitName == "GTK", xa11y-linux instead walks a bounded slice of the outer’s subtree (BFS, depth 3, restricted to roles that carry a click action, name must match) and invokes the single matching descendant it finds. Scoping is strict. It only runs inside GTK apps, only when the widget’s own Action interface is empty, and only when exactly one candidate matches. Ambiguous subtrees still surface the original error.

WebKitGTK tables

Two WebKitGTK behaviors affect <table> content (verified against WebKitGTK 2.52; both are engine behaviors, not xa11y ones):

• <th> cells can destabilize the whole page’s tree. With a window manager present, a table containing <th> header cells can send WebKit’s accessibility tree into continuous invalidation churn. Every content accessible goes defunct moments after being exposed, and the page effectively vanishes from AT-SPI. If a WebKitGTK-based app’s tree keeps coming back empty or unknown, check for this (xa11y marks dead objects with raw["atspi_defunct"]).
• Layout-table heuristic. A <table> without headers or a <caption> is judged decorative and dropped from the accessibility tree entirely. Cell text is exposed through the AT-SPI Text interface (surfaced as the cell’s value) rather than as the accessible name, so use table_cell[value*="..."] selectors for WebKitGTK content.

Linux Electron and Chromium apps

On Linux, Electron and Chromium-based apps have their AT-SPI2 bridge disabled by default for performance. xa11y will connect to the app but its tree will contain only the top-level window, so App.by_name("…").locator("button").count() returns 0 even though buttons are visible on screen.

To expose the full tree, launch the app with --force-renderer-accessibility:

# VS Code
code --force-renderer-accessibility

# Cursor
cursor --force-renderer-accessibility

# Google Chrome / Chromium
google-chrome --force-renderer-accessibility

Representative node counts on Ubuntu 24.04 + GNOME 46 (Wayland):

App	Without flag	With flag
VS Code	1	140
Cursor	1	116
Chrome	1	210

Native GTK apps (Nautilus, gnome-terminal, GNOME Calculator, gnome-text-editor) don’t need the flag, because their AT-SPI2 bridge is enabled by default.

Firefox exposes its tree when launched with MOZ_ACCESSIBILITY_ATK2=1 set in the environment.

To diagnose whether a target app has AT-SPI2 enabled at all:

busctl --user tree org.a11y.atspi.Registry | grep -i "<app-name>"

If the app’s subtree is missing, the problem is the app’s accessibility configuration, not xa11y.