gtk/docs/reference/gtk/section-accessibility.md

GTK Accessibility

The standard accessibility interface

The #GtkAccessible interface provides the accessibility information about an application's user interface elements. Assistive technology (AT) applications, like Orca, convey this information to users with disabilities, or reduced abilities, to help them use the application.

Standard GTK controls implement the #GtkAccessible interface and are thus accessible to ATs by default. This means that if you use GTK controls such as #GtkButton, #GtkEntry, or #GtkListView, you only need to supply application-specific details when the defaults values are incomplete. You can do this by setting the appropriate properties in your #GtkBuilder template and UI definition files, or by setting the properties defined by the #GtkAccessible interface.

If you are implementing your own #GtkWidget derived type, you will need to set the #GtkAccessible properties yourself, and provide an implementation of the #GtkAccessible virtual functions.

Accessible roles and attributes

The fundamental concepts of an accessible widget are roles and attributes; each GTK control has a role, while its functionality is described by a set of attributes.

Roles

Roles define the taxonomy and semantics of a UI control to any assistive technology application; for instance, a button will have a role of GTK_ACCESSIBLE_ROLE_BUTTON; an entry will have a role of GTK_ACCESSIBLE_ROLE_TEXTBOX; a toggle button will have a role of GTK_ACCESSIBLE_ROLE_CHECKBOX; etc.

Each role is part of the widget's instance, and cannot be changed over time or as the result of a user action. Roles allows assistive technology applications to identify a UI control and decide how to present it to a user; if a part of the application's UI changes role, the control needs to be removed and replaced with another one with the appropriate role.

List of accessible roles

Each role name is part of the #GtkAccessibleRole enumeration.

Role name	Description	Related GTK widget
BUTTON	A control that performs an action when pressed	#GtkButton, #GtkLinkButton, #GtkExpander
CHECKBOX	A control that has three possible value: true, false, or undefined	#GtkCheckButton
COMBOBOX	A control that can be expanded to show a list of possible values to select	#GtkComboBox
COLUMN_HEADER	A header in a columned list	#GtkColumnView
DIALOG	A dialog that prompts the user to enter information or require a response	#GtkDialog and subclasses
GRID	A grid of items	#GtkFlowBox, #GtkGridView
GRID_CELL	An item in a grid	#GtkFlowBoxChild, #GtkGridView, #GtkColumnView
IMG	An image	#GtkImage, #GtkPicture
LABEL	A visible name or caption for a user interface component	#GtkLabel
LIST	A list of items	#GtkListBox
LIST_ITEM	An item in a list	#GtkListBoxRow
METER	Represents a value within a known range	#GtkLevelBar
PROGRESS_BAR	An element that display progress	#GtkProgressBar
RADIO	A checkable input in a group of radio roles	#GtkCheckButton
ROW	A row in a columned list	#GtkColumnView
SCROLLBAR	A graphical object controlling the scrolling of content	#GtkScrollbar
SEARCH_BOX	A text box for entering search criteria	#GtkSearchEntry
SEPARATOR	A divider that separates sections of content or groups of items	#GtkSeparator
SPIN_BUTTON	A range control that allows seelcting among discrete choices	#GtkSpinButton
SWITCH	A control that represents on/off values	#GtkSwitch
TAB	A tab in a list of tabs for switching pages	#GtkStackSwitcher, #GtkNotebook
TAB_LIST	A list of tabs for switching pages	#GtkStackSwitcher, #GtkNotebook
TAB_PANEL	A page in a notebook or stack	#GtkStack
TEXT_BOX	A type of input that allows free-form text as its value.	#GtkEntry, #GtkPasswordEntry, #GtkTextView
TREE_GRID	A treeview-like columned list	#GtkColumnView
WINDOW	An application window	#GtkWindow
...	…

See the WAI-ARIA list of roles for additional information.

Attributes

Attributes provide specific information about an accessible UI control, and describe it for the assistive technology applications. GTK divides the accessible attributes into three categories:

• properties, described by the values of the #GtkAccessibleProperty enumeration
• relations, described by the values of the #GtkAccessibleRelation enumeration
• states, described by the values of the #GtkAccessibleState enumeration

Each attribute accepts a value of a specific type.

Unlike roles, attributes may change over time, or in response to user action; for instance:

• a toggle button will change its %GTK_ACCESSIBLE_STATE_CHECKED state every time it is toggled, either by the user or programmatically
• setting the mnemonic widget on a #GtkLabel will update the %GTK_ACCESSIBLE_RELATION_LABELLED_BY relation on the widget with a reference to the label
• changing the #GtkAdjustment instance on a #GtkScrollbar will change the %GTK_ACCESSIBLE_PROPERTY_VALUE_MAX, %GTK_ACCESSIBLE_PROPERTY_VALUE_MIN, and %GTK_ACCESSIBLE_PROPERTY_VALUE_NOW properties with the upper, lower, and value properties of the #GtkAdjustment

See the WAI-ARIA list of attributes for additional information.

List of accessible properties

Each state name is part of the #GtkAccessibleProperty enumeration.

State name	ARIA attribute	Value type	Notes
%GTK_ACCESSIBLE_STATE_BUSY	“aria-busy”	boolean
%GTK_ACCESSIBLE_STATE_CHECKED	“aria-checked”	#GtkAccessibleTristate	Indicates the current state of a #GtkCheckButton
%GTK_ACCESSIBLE_STATE_DISABLED	“aria-disabled”	boolean	Corresponds to the #GtkWidget:sensitive property on #GtkWidget
%GTK_ACCESSIBLE_STATE_EXPANDED	“aria-expanded”	boolean or undefined	Corresponds to the #GtkExpander:expanded property on #GtkExpander
%GTK_ACCESSIBLE_STATE_HIDDEN	“aria-hidden”	boolean	Corresponds to the #GtkWidget:visible property on #GtkWidget
%GTK_ACCESSIBLE_STATE_INVALID	“aria-invalid”	#GtkAccessibleInvalidState	Set when a widget is showing an error
%GTK_ACCESSIBLE_STATE_PRESSED	“aria-pressed”	#GtkAccessibleTristate	Indicates the current state of a #GtkToggleButton
%GTK_ACCESSIBLE_STATE_SELECTED	“aria-selected”	boolean or undefined	Set when a widget is selected

List of accessible relations

Each state name is part of the #GtkAccessibleRelation enumeration.

State name	ARIA attribute	Value type
%GTK_ACCESSIBLE_PROPERTY_AUTOCOMPLETE	“aria-autocomplete”	#GtkAccessibleAutocomplete
%GTK_ACCESSIBLE_PROPERTY_DESCRIPTION	“aria-description”	translatable string
%GTK_ACCESSIBLE_PROPERTY_HAS_POPUP	“aria-haspopup”	boolean
%GTK_ACCESSIBLE_PROPERTY_KEY_SHORTCUTS	“aria-keyshortcuts”	string
%GTK_ACCESSIBLE_PROPERTY_LABEL	“aria-label”	translatable string
%GTK_ACCESSIBLE_PROPERTY_LEVEL	“aria-level”	integer
%GTK_ACCESSIBLE_PROPERTY_MODAL	“aria-modal”	boolean
%GTK_ACCESSIBLE_PROPERTY_MULTI_LINE	“aria-multiline”	boolean
%GTK_ACCESSIBLE_PROPERTY_MULTI_SELECTABLE	“aria-multiselectable”	boolean
%GTK_ACCESSIBLE_PROPERTY_ORIENTATION	“aria-orientation”	#GtkOrientation
%GTK_ACCESSIBLE_PROPERTY_PLACEHOLDER	“aria-placeholder”	translatable string
%GTK_ACCESSIBLE_PROPERTY_READ_ONLY	“aria-readonly”	boolean
%GTK_ACCESSIBLE_PROPERTY_REQUIRED	“aria-required”	boolean
%GTK_ACCESSIBLE_PROPERTY_ROLE_DESCRIPTION	“aria-roledescription”	translatable string
%GTK_ACCESSIBLE_PROPERTY_SORT	“aria-sort”	#GtkAccessibleSort
%GTK_ACCESSIBLE_PROPERTY_VALUE_MAX	“aria-valuemax”	double
%GTK_ACCESSIBLE_PROPERTY_VALUE_MIN	“aria-valuemin”	double
%GTK_ACCESSIBLE_PROPERTY_VALUE_NOW	“aria-valuenow”	double
%GTK_ACCESSIBLE_PROPERTY_VALUE_TEXT	“aria-valuetext”	translatable string

List of accessible states

Each state name is part of the #GtkAccessibleState enumeration.

State name	ARIA attribute	Value type
%GTK_ACCESSIBLE_RELATION_ACTIVE_DESCENDANT	“aria-activedescendant”	#GtkAccessible
%GTK_ACCESSIBLE_RELATION_COL_COUNT	“aria-colcount”	integer
%GTK_ACCESSIBLE_RELATION_COL_INDEX	“aria-colindex”	integer
%GTK_ACCESSIBLE_RELATION_COL_INDEX_TEXT	“aria-colindextext”	translatable string
%GTK_ACCESSIBLE_RELATION_COL_SPAN	“aria-colspan”	integer
%GTK_ACCESSIBLE_RELATION_CONTROLS	“aria-controls”	a #GList of #GtkAccessible
%GTK_ACCESSIBLE_RELATION_DESCRIBED_BY	“aria-describedby”	a #GList of #GtkAccessible
%GTK_ACCESSIBLE_RELATION_DETAILS	“aria-details”	a #GList of #GtkAccessible
%GTK_ACCESSIBLE_RELATION_ERROR_MESSAGE	“aria-errormessage”	#GtkAccessible
%GTK_ACCESSIBLE_RELATION_FLOW_TO	“aria-flowto”	a #GList of #GtkAccessible
%GTK_ACCESSIBLE_RELATION_LABELLED_BY	“aria-labelledby”	a #GList of #GtkAccessible
%GTK_ACCESSIBLE_RELATION_OWNS	“aria-owns”	a #GList of #GtkAccessible
%GTK_ACCESSIBLE_RELATION_POS_IN_SET	“aria-posinset”	integer
%GTK_ACCESSIBLE_RELATION_ROW_COUNT	“aria-rowcount”	integer
%GTK_ACCESSIBLE_RELATION_ROW_INDEX	“aria-rowindex”	integer
%GTK_ACCESSIBLE_RELATION_ROW_INDEX_TEXT	“aria-rowindextext”	translatable string
%GTK_ACCESSIBLE_RELATION_ROW_SPAN	“aria-rowspan”	integer
%GTK_ACCESSIBLE_RELATION_SET_SIZE	“aria-setsize”	integer

Application development rules

Even if standard UI controls provided by GTK have accessibility information out of the box, there are some additional properties and considerations for application developers. For instance, if your application presents the user with a form to fill out, you should ensure that:

• the container of the form has a GTK_ACCESSIBLE_ROLE_FORM role
• each text entry widget in the form has the GTK_ACCESSIBLE_RELATION_LABELLED_BY relation pointing to the label widget that describes it

Another example: if you create a tool bar containing buttons with only icons, you should ensure that:

• the container has a GTK_ACCESSIBLE_ROLE_TOOLBAR role
• each button has a GTK_ACCESSIBLE_PROPERTY_LABEL property set with the user readable and localised action performed when pressed; for instance "Copy", "Paste", "Add layer", or "Remove"

GTK will try to fill in some information by using ancillary UI control property, for instance the accessible label will be taken from the label or placeholder text used by the UI control, or from its tooltip, if the GTK_ACCESSIBLE_PROPERTY_LABEL property or the GTK_ACCESSIBLE_RELATION_LABELLED_BY relation are unset. Nevertheless, it is good practice and project hygiene to explicitly specify the accessible properties, just like it's good practice to specify tooltips and style classes.

Application developers using GTK should ensure that their UI controls are accessible as part of the development process. When using GtkBuilder templates and UI definition files, GTK provides a validation tool that verifies that each UI element has a valid role and properties; this tool can be used as part of the application's test suite to avoid regressions.

Implementations

Each UI control implements the #GtkAccessible interface to allow widget and application developers to specify the roles, state, and relations between UI controls. This API is purely descriptive.

Each GtkAccessible implementation must provide a #GtkATContext instance, which acts as a proxy to the specific platform's accessibility API:

• AT-SPI on Linux/BSD
• NSAccessibility on macOS
• Active Accessibility on Windows

Additionally, an ad hoc accessibility backend is available for the GTK testsuite, to ensure reproducibility of issues in the CI pipeline.

Authoring practices

The authoring practices are aimed at application developers, as well as developers of GUI elements based on GTK.

Functionally, #GtkAccessible roles, states, properties, and relations are analogous to a CSS for assistive technologies. For screen reader users, for instance, the various accessible attributes control the rendering of their non-visual experience. Incorrect roles and attributes may result in a completely inaccessible user interface.

A role is a promise

The following code:

gtk_widget_class_set_accessible_role (widget_class, GTK_ACCESSIBLE_ROLE_BUTTON);

is a promise that the widget being created will provide the same keyboard interactions expected for a button. An accessible role of a button will not turn automatically any widget into a #GtkButton; but if your widget behaves like a button, using the %GTK_ACCESSIBLE_ROLE_BUTTON will allow any assistive technology to handle it like they would a #GtkButton.

Attributes can both hide and enhance

Accessible attributes can be used to override the content of a UI element, for instance:

gtk_label_set_text (GTK_LABEL (label), "Some text");
gtk_accessible_update_property (GTK_ACCESSIBLE (label),
				GTK_ACCESSIBLE_PROPERTY_LABEL,
				"Assistive technologies users will perceive "
				"this text, not the contents of the label",
				-1);

In the example above, the "label" property will override the contents of the label widget.

The attributes can also enhance the UI:

gtk_button_set_label (GTK_BUTTON (button), "Download");
gtk_box_append (GTK_BOX (button), button);

gtk_label_set_text (GTK_LABEL (label), "Final report.pdf");
gtk_box_append (GTK_BOX (box), label);

gtk_accessible_update_relation (GTK_ACCESSIBLE (button),
				GTK_ACCESSIBLE_RELATION_LABELLED_BY,
				g_list_append (NULL, label),
				-1);

In the example above, an assistive technology will read the button's accessible label as "Download Final report.pdf".

The power of hiding and enhancing can be a double-edged sword, as it can lead to inadvertently overriding the accessible semantics of existing widgets.

Design patterns and custom widgets

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