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focusgroup for HTML and CSS

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Authors: Travis Leithead, David Zearing, Chris Holt

Status of this Document

This document is a starting point for engaging the community and standards bodies in developing collaborative solutions fit for standardization. As the solutions to problems described in this document progress along the standards-track, we will retain this document as an archive and use this section to keep the community up-to-date with the most current standards venue and content location of future work and discussions.

This document status: ARCHIVED
Current venue: Open UI Community Group
Current version: https://open-ui.org/components/focusgroup.explainer

1. Introduction

When writing custom controls, authors need to implement the semantics of various known controls (see ARIA authoring guide) to enable proper (and expected) keyboard support. Control examples include tabs and tabsets, combo boxes, accordion panels, carousels, focusable grid tables, etc. Many of these patterns expect arrow-key navigation, as well as support for page down/up, home/end, even "type ahead" behavior.

The native web platform supports some of these linear navigation behaviors in native controls like radio button groups (wrap-around arrow key movement that changes both focus and linked selection), <select> element popups (up/down movement among options), and date-time controls (arrow key movement among the components of the date), but does not expose a primitive that can be used independently to get this behavior.

We propose exposing a new web platform primitive—'focusgroup'—to facilitate focus navigation (not selection) using arrow keys among a set of focusable elements. This feature can then be used (without any JavaScript) to easily supply platform-provided focusgroup navigation into custom-authored controls in a standardized and predictable way for users.

Customers like Microsoft's Fluent UI team are excited to leverage this built-in capacity for its keyboard consistency, default accessibility (provides a signal to ATs for alternate keyboard navigation), and promised interoperability over existing solutions.

While this document emphasizes the usage of the keyboard arrow keys for accessibility navigation, we acknowledge that there are other input modalities that work (or can be adapted to work) equally well for focusgroup navigation behavior (e.g., game controllers, gesture recognizers, touch-based ATs, etc.)

2. Goal

The goal of this feature is to "pave the cow path" of an existing authoring practice (and accessibility best-practice) implemented in nearly every Web UI library: the "roving tabindex". Here's a few sources that explain roving tabindex in more detail as well as a selection of common libraries implementing the pattern:

To achieve this goal, we believe that the solution must be done with declarative markup or CSS. If JavaScript is required, then there seems little advantage to using a built-in feature over what can be implemented completely in author code. Furthermore, a declarative solution provides the key signal that allows the platform's accessibility infrastructure to make the group accessible by default:

Signaling to the AT that arrow-key navigation can be used on the focused element.
Understanding the bounds/extent of the group, providing list context like "X in Y items" (posinset/setsize)
Providing a consistent and reliable navigation usage pattern for users with no extra author code required.

3. Non-Goals

In most roving tabindex implementations, the notion of moving focus is tightly coupled with the notion of selection. In some cases, it makes sense to have selection follow the focus, but in other scenarios these need to be decoupled. For this proposed standard, we decouple selection from focus and only focus (cough) on the focus aspect: moving focus using the keyboard among eligible focus targets. Adding selection state, e.g., tracking the currently selected option in a list, will be a separate feature. To handle selection-based scenarios, we defer to the CSS proposal Toggles which can work nicely with focusgroups.

No additional UI (e.g., a "focus ring") is associated with focusgroups. A focusgroup is wholly intended as a logical (transparent) grouping mechanism for a set of already focusable child elements, providing arrow key navigation among them. All the pre-existing styling/ native UI affordances for focus tracking are unchanged with this proposal.

4. Principles

Intuitive use in declarative scenarios. Focusgroups
- are easy to reason about (self-documenting) in the source markup or CSS.
- provide an intuitive interaction between focusgroups.
- integrate well with other related platform semantics.
Focusgroups are easy to maintain and configure.
- Configuration is managed in one place.
- Provide easy to understand usage into HTML and CSS patterns.
- Avoid "spidery connections" e.g., using IDRefs or custom names that are hard to maintain.
Complimentary declarative representations in HTML and CSS
- HTML attributes offers focusgroup usage directly with impacted content and provide for the most straightforward scenarios.
- CSS properties allow for responsive design patterns to conditionally apply focusgroup behavior under changing layouts. Enables some advanced use cases where selector-based matching is advantageous.

5. Use Cases

(Child opt-in) Group a set of focusable child elements under a single focusgroup.
(Descendent opt-in) Focusable elements deeply nested can participate in a single focusgroup.
(Wrap) Focusgroup can be configured to have wrap-around focus semantics.
(Horizontal/vertical) A focusgroup can be configured to respond to either horizontal navigation keys or vertical keys or both (to trivially reserve one axis of arrow key behavior for supplementary actions, such as opening nodes in a tree view control).
(Extend same direction) Focusgroups can be nested to provide arrow navigation into multiple composed widgets (such as lists within lists).
(Extend opposite direction) Focusgroups can be nested to provide arrow navigation into composed widgets with orthogonal navigation semantics (such as horizontal-inside-vertical menus).
(Multiple focusgroups) Multiple focusgroups can be established on a single element (advanced CSS scenario).
(Opt-out) Individual elements can opt-out of focusgroup participation (advanced CSS scenario)
(Grid) Focusgroups can be used for grid-type navigation (<table>-structured content or other grid-like structured content (advanced CSS scenario), but not "presentation" grids).

6. Focusgroup Concepts

A focusgroup is a group of elements that are related by arrow-key navigation and for which the web platform provides the arrow key navigation behavior by default (no JavaScript event handlers needed)! Navigation is provided according to order or structure of the DOM (not how the content is presented in a user interface).

This document describes two kinds of focusgroups: linear focusgroups and grid focusgroups. Linear focusgroups provide arrow key navigation among a list of elements. Grid focusgroups provide arrow key navigation behavior for tabular (or 2-dimensional) data structures.

Multiple linear focusgroups can be combined together into one logical focusgroup, but linear focusgroups cannot be combined with grid focusgroups and vice-versa (and grid focusgroups cannot be combined with each other).

Focusgroups consist of a focusgroup definition that establish focusgroup candidates and focusgroup items. Focusgroup definitions manage the desired behavior for the associated focusgroup items. Focusgroup items are the elements that actually participate in the focusgroup (among the possible focusgroup candidates).

When a linear focusgroup definition is associated with an element, all of that element's direct children become focusgroup candidates. Focusgroup candidates become focusgroup items if they are focusable, e.g., implicitly focusable elements like <button>, or explicitly made focusable via tabindex or some other mechanism (e.g., contenteditable).

In HTML, one focusgroup definition can be added to an element using the focusgroup attribute:

Example 1:

<p id=parent focusgroup>
   Some text
   <a id=one href="…">a link</a>.
   Some more text.
   <span id=two tabindex=-1> focusable span</span>.
   <a id=three href="…">another link</a>
</p>

Using CSS, a focusgroup definition can be applied with selectors, and must include a name. auto is a reserved name that corresponds to the same focusgroup implied by the HTML focusgroup attribute.

#parent { 
   focus-group: auto;
}

For the parent element which includes the focusgroup definition, the elements one, two, and three (and any other children of parent that may be added or removed) are focusgroup candidates and because each are focusable, they also become focusgroup items. When one of the focusgroup items is focused, then the user can move focus sequentially according to DOM order among all the focusgroup items using the arrow keys (up/right moves focus forward, down/left moves focus backwards). Note that only elements one and three can be focused using the Tab key (because element two has tabindex=-1 set, which takes it out of the tabindex sequential navigation ordering).

Focusgroup definitions may include the following (in addition to a name):

extend -- applies to linear focusgroups only: a mechanism to join this linear focusgroup to an ancestor linear focusgroup.
direction -- applies to linear focusgroups only: constrains the keys used for arrow key navigation to horizontal, vertical, or both (the default).
wrap -- what to do when the attempting to move past the end of a focusgroup. The default/initial value is nowrap which means that focus is not moved past the end of a focusgroup with the arrow keys.

In HTML these focusgroup definitions are applied as space-separated token values to the focusgroup attribute. In CSS, these definitions are specified as properties (including a focus-group shorthand property for convenience).

Example 1b:

<div focusgroup="wrap horizontal">

Example 1c:

div { 
   focus-group-name: auto;
   focus-group-wrap: wrap;
   focus-group-direction: horizontal;
}

In the case that HTML attribute values conflict with CSS properties, the CSS values override the HTML-defined values. For example:

Example 1d:

<div focusgroup="wrap horizontal" style="focus-group-name: auto; focus-group-wrap: nowrap; focus-group-direction: both">

The CSS-specified value of 'nowrap' would override the HTML attribute value's "wrap" directive; similarly for 'both' overriding "horizontal".

There is no change to the way Tab navigation works with tabindex nor the Tab ordering behavior. To use a focusgroup, focus must enter that element's focusable children somehow: for accessibility and keyboard-only scenarios, the Tab key is typically used--programmatic calls to element.focus() or user clicks with a pointing device are alternatives.

The focusgroup can be used to reduce the number of tab stops (tabindex=0) necessary in a document by converting those into tabindex=-1 and adding a focusgroup to manage them. The 'roving tabindex' scenario is accomplished by picking an entry point to the focusgroup (a child with tabindex=0), and setting the rest of the focusable elements to tabindex=-1. This is the same pattern needed to setup the roving tabindex, but by adding focusgroup, no JavaScript is necessary to manage it afterward:

Example 2:

<my-list focusgroup>
  <my-listitem tabindex="0">...</mylistitem>
  <my-listitem tabindex="-1">...</mylistitem>
  <my-listitem tabindex="-1">...</mylistitem>
  <my-listitem tabindex="-1">...</mylistitem>
  <my-listitem tabindex="-1">...</mylistitem>
</my-list>

From outside of the above markup, assume a Tab key press lands focus on the first <my-listitem>. From this point, the user can use the arrow keys to move from the beginning of the list to the end, or press Tab again to move outside of this group. Alternatively, maybe you want to support both Tab and Arrow key navigation in your scenario. No problem, just change the setup so that all the list items participate in the tab order:

Example 3:

<my-list focusgroup>
  <my-listitem tabindex="0">...</mylistitem>
  <my-listitem tabindex="0">...</mylistitem>
  <my-listitem tabindex="0">...</mylistitem>
  <my-listitem tabindex="0">...</mylistitem>
  <my-listitem tabindex="0">...</mylistitem>
</my-list>

The focusgroup doesn't "remember" the last element that was focused when focus leaves the group and returns later. Instead, the "leaving" and "returning" logic (for keyboard scenarios) depends on the preexisting tabindex sequential focus navigation only (those with tabindex=0 for example). The CSS Toggles proposal could be used in this same scenario to track the "toggle state" among this group of toggle-able elements, allowing focus changes to be decoupled from "selection/toggle" state.

A future extension of this proposal may allow focus entering a focusgroup to jump to the currently toggled (or the toggle with the highest value) if any toggles are set in the focusgroup.

6.1. Key conflicts

The focusgroup handles keystrokes (keydown) with a default behavior to move the focus within focusgroup items. This default keyboard handling could interfere with other actions the application would like to take. Therefore, authors may cancel the focusgroup's default behavior by canceling (preventDefault()) on the keydown event. These events will be dispatched by the focused element, and bubble through the focusgroup parent element, which is a convenient place to handle the event.

6.2. Key traps

Some built-in controls like <input type=text> "trap" nearly all keys that would be handled by the focusgroup. This proposal does not provide a way to prevent this from happening (Tab should continue to be used to "exit" these trapping elements).

6.3. Enabling wrapping behaviors

By default, focusgroup traversal with arrow keys ends at boundaries of the focusgroup (the start and end of a linear focusgroup, and the start and end of both rows and columns in a grid focusgroup). The following focusgroup definition values can configure this:

HTML attribute value	CSS property & value	Explanation
focusgroup="wrap"	focus‑group‑wrap: wrap	linear focusgroup: causes movement beyond the ends of the focusgroup to wrap around to the other side; grid focusgroup: causes focus movement at the ends of the rows/columns to wrap around to the opposite side of the same rows/columns
focusgroup="" (unspecified)	focus‑group‑wrap: nowrap	Disables any kind of wrapping (the initial/default value)

The following are only applicable to grid focusgroups. Note, row and column-specific wrapping and flowing can be specified together: focus-group-wrap supports two-token specifiers for this purpose.

HTML attribute value	CSS property & value	Explanation
focusgroup="row‑wrap"	focus‑group‑wrap: row‑wrap	Rows wrap around, column wrapping [and flowing as described below] is disabled.
focusgroup="col‑wrap"	focus‑group‑wrap: col‑wrap	Columns wrap around, but row wrapping [and flowing as described below] is disabled.
focusgroup="row‑wrap col‑flow	focus‑group‑wrap: row‑wrap col‑flow	Rows wrap around, and columns flow (as described below). Similar combination possible for `row-flow` and `col-wrap`. Using `row-wrap` and `col-wrap` is equivalent to specifying `wrap`
focusgroup="flow"	focus‑group‑wrap: flow	Movement past the end of a row wraps the focus to the beginning of the next row. Movement past the beginning of a row wraps focus back to the end of the prior row. Same for columns. The last row/column wraps to the first row/column and vice versa.
focusgroup="row‑flow"	focus‑group‑wrap: row‑flow	Rows "flow" from row ends to the next/prior row as described above, but column flowing/wrapping is disabled.
focusgroup="col‑flow"	focus‑group‑wrap: col‑flow	Columns "flow" from column ends to the next/prior column as described above, but row flowing/wrapping is disabled.

6.4. Expanding and connecting linear focusgroups together (`extend`)

By default, a focusgroup definition's focusgroup candidates are its direct children. There are two ways to "extend the reach" of a linear focusgroup's candidates. One way is to use CSS to directly assign a focusgroup candidate state to a descendant element (explained later). The other is to use extend. A linear focusgroup definition can declare that it intends to extend an ancestor linear focusgroup. If there is an ancestor linear focusgroup of the same name, the extending focusgroup becomes an extension of that ancestor's focusgroup. Extending a linear focusgroup is also an opportunity to change the directionality (and, conditionally, the wrapping) of the newly extended focusgroup candidates (as described later).

Using extend in a focusgroup definition is only valid for linear focusgroups. Grid focusgroups cannot use extend to become a part of linear focusgroup. Similarly, linear focusgroups cannot use extend to become part of a grid focusgroup. And grid focusgroups cannot use extend to join an ancestor grid focusgroup.

Below, the <my-accordion> element with a focusgroup attribute defines a focusgroup with nothing focusable in it; the focusable <button> elements are separated by an <h3> element. The <h3> and <div> elements are the focusgroup candidates, and are not focusable:

Example 4:

<my-accordion focusgroup>
  <h3><button aria-expanded=true aria-controls=p1>Panel 1</button></h3>
  <div id=p1 role=region>Panel 1 contents</div>
  <h3><button aria-expanded=true aria-controls=p2>Panel 2</button></h3>
  <div id=p2 role=region>Panel 2 contents</div>
</my-accordion>

To make the <button>s belong to one focusgroup, a focusgroup definition must placed on the <h3> elements that explicitly declares extend, causing <h3> children to become focusgroup candidates.

Example 5:

my-accordion[focusgroup] > h3 {
   focus-group-name: auto extend;
}

The extend value employs an ancestor lookup to attempt to locate-and-extend a same-named linear focusgroup. It is not necessary that an extending linear focusgroup be a direct child of an existing focusgroup. The first-located focusgroup definition in the ancestor chain of elements is the focusgroup definition that is considered for extending.

When extending a focusgroup, traversal order is based on document order. Given the following:

Example 6:

<div focusgroup> 
  <div id=A tabindex=0></div> 
  <div id=B tabindex=-1>
    <div>
      <div focusgroup=extend>
        <div id=B1 tabindex=-1></div> 
        <div id=B2 tabindex=-1></div>
      </div>
    </div>
  </div> 
  <div id=C tabindex=-1></div> 
</div>

Sequentially pressing the right arrow (assuming horizontal-tb + LTR writing-mode) would move through the <div>s: A, B, B1, B2, C. (And in reverse direction: C, B2, B1, B, A, as expected.)

When the extending linear focusgroup is axis-aligned (see following sections), the wrapping state of an ancestor focusgroup definition is applied to it. For example: specifying wrap on an extending focusgroup definition when "nowrap" (even implicitly) was specified on a parent focusgroup (of the same supported axis) does not make sense; the extending focusgroup candidates join the rest of the ancestor focusgroup candidates to form one logical ordering--they do not define a separate range of focusgroup candidates to apply different wrapping logic onto.

Example 7:

<!-- This is an example of what NOT TO DO -->
<div focusgroup> 
  <div id=A tabindex=0></div> 
  <div id=B tabindex=-1 focusgroup="extend wrap"> <!-- 'wrap' will not apply -->
    <div id=B1 tabindex=-1></div> 
    <div id=B2 tabindex=-1></div> 
  </div> 
  <div id=C tabindex=-1></div> 
</div>

In this, wrap specified on the extending focusgroup definition will not cause any wrapping behavior to apply. The extending focusgroup (id=B) extended a "nowrap" state from its ancestor focusgroup and will use that value regardless of the presence of wrap.

6.5. Limiting linear focusgroup directionality

In many cases, having multi-axis directional movement (both right arrow and down arrow linked to the forward direction) is not desirable, such as when implementing a tablist, and it may not make sense for the up and down arrows to also move the focus left and right. Likewise, when moving up and down in a vertical menu, the author might wish to make use of the left and right arrow keys to provide behavior such as opening or closing sub-menus. In these situations, it makes sense to limit the linear focusgroup to one-axis traversal.

Note that the following only apply to linear focusgroup definitions (they have no effect on grid focusgroups).

HTML attribute value	CSS property & value	Explanation
focusgroup="horizontal"	focus‑group‑direction: horizontal	The focusgroup items will respond to forward and backward movement only with the "horizontal" arrow keys (left and right).
focusgroup="vertical"	focus‑group‑direction: vertical	The focusgroup items will respond to forward and backward movement only with the "vertical" arrow keys (up and down).
focusgroup="" (unspecified)	focus‑group‑direction: both	The focusgroup items will respond to forward and backward movement with both directions (horizontal and vertical). The default/initial value.

Example 8:

<style>
  tab-group { 
     focus-group-name: auto;
     focus-group-direction: horizontal;
     focus-group-wrap: wrap;
  }
</style>
<!-- ... -->
<tab-group role=tablist> 
  <a-tab role=tab tabindex=0>…</a-tab> 
  <a-tab role=tab tabindex=-1>…</a-tab> 
  <a-tab role=tab tabindex=-1>…</a-tab> 
</tab-group>

In the above example, when the focus is on the first <a-tab> element, pressing either the up or down arrow key does nothing because the focusgroup is configured to only respond to the left/right arrow keys.

Because 2-axis directionality is the default, specifying both horizontal and vertical at the same time on one focusgroup is not allowed:

Example 9:

<!-- This is an example of what NOT TO DO -->
<radiobutton-group focusgroup="horizontal vertical wrap"> 
  This focusgroup configuration is an error--neither constraint will be applied (which is actually 
  what the author intended).
</radiobutton-group>

6.6. Interactions with directionality + extending

Powerful scenarios are possible when extending single-axis linear focusgroups. For example, authors can create tiles that are navigated with left and right arrow keys, and within each tile use sub-menus that are navigated with the up and down keys (all in one logical focusgroup!). Vertical email lists can be navigated with up and down keys, while email actions can be easily accessed with right and left keys. Alternating horizontal and vertical interactions can be combined arbitrarily deep in the DOM.

When a focusgroup extends another focusgroup, it never extends the parent's directionality values (horizontal or vertical). Each extending focusgroup declares (or take the default) directionality.

6.6.1. Axis-aligned extending linear focusgroups

When a focusgroup is processing an arrow keypress, if it has an extending focusgroup that supports the direction requested, then the arrow keypress is forwarded to that focusgroup. When the axes are aligned, this is how the focusgroup is extended into a contiguous linear group as described previously.

Example 10:

<vertical-menu focusgroup="vertical wrap">
  <menu-item tabindex="-1">Action 1</menu-item>
  <menu-item tabindex="0">Action 2</menu-item>
  <menu-group focusgroup="vertical extend">
    <menu-item tabindex="-1">Sub-Action 3</menu-item>
    <menu-item tabindex="-1">Sub-Action 4</menu-item>
  </menu-group>
  <menu-item tabindex="-1">Action 5</menu-item>
</vertical-menu>

Because the parent and the extending focusgroup are axis-aligned, they form an extended linear focusgroup.

6.6.2. Orthogonal-axis extending linear focusgroups

Example 11:

<style>
  horizontal-menu {
    focus-group-name: auto;
    focus-group-direction: horizontal;
    focus-group-wrap: wrap;
  }
  omni-menu {
    focus-group-name: auto extend;
  }
</style>
<!-- ... -->
<horizontal-menu>
  <menu-item tabindex="-1">Action 1</menu-item>
  <menu-item tabindex="0">Action 2</menu-item>
  <container-element tabindex="-1">
    <omni-menu>
      <menu-item tabindex="-1">Sub-Action 3</menu-item>
      <menu-item tabindex="-1">Sub-Action 4</menu-item>
    </omni-menu>
  </container-element>
  <menu-item tabindex="-1">Action 5</menu-item>
</horizontal-menu>

The above is an example of a vertical menu nested inside of a horizontal menu. When "Action 2" is focused and a down arrow key is pressed, the <horizontal-menu> focusgroup ignores the key because it is configured to only handle horizontal keys. However, when focus moves to the <container-element> and a down arrow key is pressed, the <omni-menu>'s extending focusgroup (a child of the currently focused element) supports the given axis ('both' axes is the initial value), and so the focus is moved "forward" to "Sub-Action 3". What was different in this case, is that the down arrow key which was not supported by the <horizontal-menu>'s focusgroup definition, was handled by the <omni-menu>'s focusgroup.

The above is a descent operation.

Interestingly, this configuration is not bi-directional. Once focus has descended into the <omni-menu>'s focusgroup the down arrow key (when focus is on "Sub-Action 4") cannot be used to continue to the <horizontal-menu>'s "Action 5" because the <horizontal-menu>'s focusgroup will reject that axis. Conversely, with "Sub-Action 3" focused, the up arrow key will not move focus to the <omni-menu> element because the vertical axis arrow keys are rejected by the owning <horizontal-menu>'s focusgroup.

Once descended into the <omni-menu>'s focusgroup, the way to ascend again is through an arrow keypress that is axis-aligned with the parent's focusgroup (when focus is at the start or end of the child's focusgroup since the child's focusgroup handles both axes). Continuing with Example 11 and "Sub-Action 3" focused, a left arrow key press (reverse direction) causes an ascension into the parent's focusgroup (focusing the <container-element> element). Similarly, when "Sub-Action 4" is focused, a right arrow key will cause an ascension to the parent's focusgroup and focus "Action 5". The horizontal axis is aligned between the focusgroups and so horizontal arrow key requests are extensions of the parent's focusgroup, while vertical arrow key presses stay "stuck" in the child focusgroup.

When extending focusgroups have orthogonal directionality they create ascender or descender relationships.

The arrow key interactions will be clearer to users when nested focusgroups are strictly orthogonal to each other. Authors should not extend both direction linear focusgroups with single-directional linear focusgroups (and vice-versa) as a best practice. The following example is a best-practice:

Example 12:

<horizontal-menu focusgroup="horizontal wrap">
  <menu-item tabindex="-1">Action 1</menu-item>
  <menu-item tabindex="0">Action 2</menu-item>
  <vertical-menu tabindex="-1" focusgroup="vertical extend">
    <menu-item tabindex="-1">Sub-Action 3</menu-item>
    <menu-item tabindex="-1">Sub-Action 4</menu-item>
  </vertical-menu>
  <menu-item tabindex="-1">Action 5</menu-item>
</horizontal-menu>

When focus is on the <vertical-menu> focusgroup item, only a down arrow key will descend into the nested focusgroup (not a right arrow key because this is disallowed by the vertical extending focusgroup). Similarly, only a left arrow key will ascend from "Sub-Action 3" focusgroup item back to the <vertical-menu> focusgroup item. Using alternating directions in nested focusgroups ensures natural symmetry for users (cross-axis forward to descend, cross-axis reverse to ascend).

When a focusgroup is considering a cross-axis arrow key to descend, only the currently focused element and any of its extending focusgroup descendants are considered. This behavior ensures that no unexpected descents occur when focus is not on a currently descendible element. Conversely, any of a focusgroup's focused children will check the parent focusgroup for a cross-axis ascent (if that axis is not already handled by the current focusgroup--and if it is handled, only the extremities of the focusgroup's children perform this check as in Example 11). This means that ascending to the parent focusgroup is possible from any extending children.

6.6.3. Notes about wrapping while extending

As noted previously, the wrapping state of a focusgroup definition is extended only when two focusgroups have an axis-aligned relationship:

Example 13:

<!-- attributes making these elements focusable are elided -->
<div focusgroup=wrap>
  <span focusgroup=extend>…</span> 
</div>

Both the <div> and <span> have focusgroups configured with default 2-axis directionality. Both sets of axes are aligned, and so the wrap value is extended down and cannot be overridden by the <span>'s focusgroup definition. (Because the axes are aligned, they are an extended linear focusgroup. As one logical linear focusgroup, it does not make sense to try to change the wrapping behavior for a subset of the focusgroup.)

Example 14:

<div focusgroup=wrap> 
  <span focusgroup="extend horizontal">…</span> 
</div>

The above is a case where the focusgroups make an extended linear focusgroup in the horizontal direction (wrap state cannot be changed by the child for the horizontal direction), and a descender/ascender relationship in the vertical direction (it's one-way: from the <span> to the <div> not vice-versa). But because the <span>'s focusgroup definition does not support the vertical direction, wrapping state is not extended from the parent. Conversely:

Example 15:

<style>
  div  { focus-group: auto wrap horizontal; }
  span { focus-group: auto extend; }
</style>
<!-- ... -->
<div> 
  <span>…</span> 
</div>

The focusgroups are axis aligned in the horizontal direction (wrap in the horizontal direction cannot be changed by the child), and a descender/ascender relationship in the vertical direction (also one-way from <div> to <span> and not vice-versa). The <span>'s focusgroup supports a direction (vertical) that it doesn't extend from the <div>'s focusgroup and so vertical arrow keys (while focused inside the <span>'s focusgroup) can be independently configured to wrap or not wrap (in Example 15 they won't wrap because nowrap is the initial value). In Example 16, the up/down arrow keys will wrap around (exclusively) in the <span>'s focusgroup, but not when using the left/right arrow keys:

Example 16:

<style>
  /* spacing aligned for comparison */
  div  { focus-group: auto        nowrap horizontal; }
  span { focus-group: auto extend wrap   both; }
</style>
<!-- ... -->
<div> 
  <span>…</span> 
</div>

When the relationships are descender/ascender in both directions, then the wrap state can't extend in any direction, and will apply to each focusgroup's chosen direction independently:

Example 17:

<style>
  /* spacing aligned for comparison */
  div  { focus-group: auto        horizontal nowrap; }
  span { focus-group: auto extend vertical   wrap; }
</style>
<!-- ... -->
<div> 
  <span>…</span> 
</div>

6.6.4. Deep combinations

Nesting focusgroups can be applied to arbitrary depths to create either extended linear groups or ascender/descender relationships as needed--all forming a single logical focusgroup. Consider vertical menus (3) inside of cards oriented horizontally (2) nested inside of rows structures (1):

Structurally:

Example 18:

<style>
   table-row, card-view, .somestructure { focus-group-name: auto extend; }
   table-row { focus-group-direction: horizontal; }
   card-view, .somestructure { focus-group-direction: vertical; }
   table-row, card-view { focus-group-wrap: wrap; }
</style>
<!-- ... -->
<data-table focusgroup=vertical> 
  <table-row tabindex=-1> 
    <card-view tabindex=-1> 
      <focusable-entry tabindex=-1></focusable-entry> 
      <div class=somestructure> 
        <focusable-entry tabindex=-1></focusable-entry> 
        <focusable-entry tabindex=-1></focusable-entry> 
      </div> 
    </card-view> 
    …n card-view similar siblings 
  </table-row> 
  …m table-row similar siblings 
</data-table>

In this example, the <data-table>'s rows can be navigated with up/down arrows. When the user has focused a row they would like to explore, the right arrow key moves them into the <card-view> items in the row, and they can use left and right arrow keys (that wrap around start-to-end) to cycle through the cards. If desired, while at any card, the up arrow will take them back to the parent <table-row> to move up/down to the next row. Alternatively, while looking at a card with a nested vertical list, they can press the down arrow to descend into the first <focusable-entry> in the list items, and cycle through them (with wrapping). The <focusable-entry> elements have some <div> support structure in the markup. To "unify" the <focusable-entry>s into one logical list for arrow navigation, the focusgroup on the <div> just extends in the same direction as the parent (and the wrapping value is also extended).

6.7. Opting-in & opting-out

Focusgroup definitions are assigned to an element in order to set the behavior for their child elements which become focusgroup candidates. Because all child elements are focusgroup candidates, any child element that is (or becomes) focusable will automatically become a focusgroup item belonging to it's parent's focusgroup.

What if an element should be focusable, exists as a child of an element with a focusgroup definition (because some of its other focusable siblings should belong to the focusgroup), but does not want to participate in the focusgroup?

Conversely, what if an element that is not a direct child of a linear focusgroup (but is a descendant) would like to become a member of a focusgroup without using extend?

Individual focusgroup candidates can "opt-out" or "opt-in" to participation in any focusgroup. Opting-in or out is a local focusgroup item decision (it is not be managed at the focusgroup definition attached to the parent element). In order for a focusgroup item to opt-in or out, a new (local) mechanism is needed.

In this proposal, there is no way for a focusgroup candidate to opt-in or out using HTML alone (a proposal would likely require a new attribute with different focusgroup semantics, and opt-in or opt-out scenarios are considered edge-cases).

To opt-in or opt-out, a CSS property is used, which applies only to focusgroup candidates (not focusgroup definitions):

CSS property & value	Explanation
focus‑group‑item: auto	Opt-in to a focusgroup: this element becomes a focusgroup candidate for the nearest ancestor that defines a linear focusgroup matching `auto`. The element will "search" its parent nodes looking for a matching focusgroup definition and will become an "extension" of that group (i.e., similar to using `extend`, but without the opportunity to re-establish a new focusgroup definition)
focus‑group‑item: none	Opt-out of a focusgroup: this element will not participate in any focusgroup. (`none` is the initial value when there is no focusgroup definition on a parent element; `auto` is the initial value when there is a parent focusgroup definition.)

In the following example, the options-widget opts-out of participation in the focusgroup.

Example 19:

<style>
  #container { focus-group: auto; }
  .optout { focus-group-item: none; }
</style>
<!-- ... -->
<control-row id=container>
  <options-widget class=optout> ... </options-widget>
  <action-button>...</action-button>
  <action-button>...</action-button>
  <action-button>...</action-button>
  <action-button>...</action-button>
</control-row>

In the following example, the element opts-in to the focusgroup defined on "ancestor".

Example 20:

<style>
  #ancestor { focus-group: auto; }
  .optin { focus-group-item: auto; }
</style>
<!-- ... -->
<div id=ancestor>
  <div>
    <div>
      <div>
        <div>
          <deep-child class=optin>...</deep-child>
        </div>
      </div>
    </div>
  </div>
</div>

6.8. Multiple focusgroups among siblings

Similar to how some focusgroup candidates can opt-in or opt-out (see prior section), other focusgroup candidates among a set of sibling elements may desire to participate in a separate focusgroup from their other siblings.

We elect to only provide this advanced scenario with CSS. Using focus-group-item, a focusgroup candidate can specify the custom identifier of a matching parent focusgroup definition it would like to belong to (assuming it is focusable).

CSS quite easily allows multiple focusgroup definitions to be applied to a single container element via custom identifiers (this would be less elegant with HTML attributes). The name auto (and the grid focusgroup name) is reserved, but other values are treated as custom identifiers and define new focusgroup definitions that focusgroup candidates can opt-into.

Note: a focusgroup candidate can only be in one focusgroup at a time, and the focusgroup it belongs to is the one specified by its focus-group-item value.

CSS property & value	Explanation
focus‑group‑name: <custom ident>	Gives the focusgroup a custom identifiers. Only focusgroup candidates that opt-in to this named identifier will belong to this focusgroup.
focus‑group‑item: <custom ident>	Declares this focusgroup candidate's intention to belong to a focusgroup definition with the given identifier. If there is no matching focusgroup definition with this name in its ancestry, then this is an error and this item will revert to focus-group-item: `none` (or `auto` if it is a child of an element defining a linear focusgroup.
focus‑group‑name, focus‑group‑direction, and focus‑group‑wrap	Each allows comma-separated list to accommodate multiple definitions.

The following example shows one parent element that has two focusgroups defined, and opts half of the children into one and half into the other.

Example 21:

<style>
  tabs { 
    focus-group-name: redtab, bluetab;
    focus-group-direction: horizontal, horizontal;
  }
  .redtab { focus-group-item: redtab; }
  .bluetab { focus-group-item: bluetab; }
</style>
<!-- ... -->
<tabs focusgroup>
  <tab class=redtab>...</tab>
  <tab class=redtab>...</tab>
  <tab class=redtab>...</tab>
  <tab class=bluetab>...</tab>
  <tab class=bluetab>...</tab>
  <tab class=bluetab>...</tab>
</tab>

6.9. Grid focusgroups

Some focusable data is structured not as a series of nested linear groups, but as a 2-dimensional grid such as in the Excel app, where focus can move logically from cell-to-cell either horizontally or vertically. In these data structures, it makes sense to support the user's logical usage of the arrow keys to move around the data.

Grid navigation is expected to happen within well-structured content with consistent rows and columns where DOM structure reflects this organization.

6.9.1. Applicability to tabular data

The arrow navigation in the grid (and in the previous non-grid scenarios) should reflect the accessible structure of the document, not the presentation view made possible with CSS. For example, it is easy to create views that visually appear grid-like, but do not make sense to navigate like a grid if considering that the data model is fundamentally a list, which is how users of accessibility technology would perceive it. Wrapping a list of contact cards on screen in a grid-like presentation allows for more content density on screen for sighted users. In that scenario, arrow key navigation to move linearly (left-to-right following the line-breaking across each line) through the contents makes sense (especially if these are alphabetized), but orthogonal movement through the "grid" (up/down when cards are aligned or in a masonry layout) jumps the focus to seemingly arbitrary locations. Multi-directional arrow key navigation may seem appropriate for sighted users that have the visual context only, but are not appropriate for assistive technology. In the case of the list-presented-as-a-grid scenario, a linear focusgroup will make the most sense for sighted as well as users with accessibility needs.

When considering using a grid focusgroup, be sure that the data is structured like a grid and that the structure makes semantic sense in two dimensions (and not just for a particular layout or presentation).

Tabular data can be structured using column-major or row-major organization. Given that HTML tables and ARIA attributes for grids (role=grid, role=row, role=gridcell) only exist for row-major grid types, this proposal does not define grid focusgroup organization for column-major data structures (and assumes row-major data structures throughout).

6.9.2. Grid isolation

As noted previously the extend value is not applicable to grid focusgroups, and grid focusgroups cannot be combined with linear focusgroups. While it is obviously possible to create linear focusgroups inside of a grid cell data structure, and vice-versa (a grid as a value of a list), this proposal does not allow these different focusgroup types to be connected automatically. Some additional scripting may be necessary to add explicit "cell enter/exit" behavior (or just use the Tab key).

6.9.3. Setting up a grid focusgroup

Grid focusgroups can be created "automatically" or manually. HTML only supports the "automatic" grid, while CSS can be used to do the same or to manually describe the parts of the grid.

Automatic grids use the context of existing HTML semantics for tables as the structural components necessary to provide grid-based navigation. Any elements with computed table layout are suitable for an automatic grid (e.g., display: table-row in place of using a <tr> elements).

(We are evaluating the suitability for other grid-like patterns including CSS display: grid or ARIA role=grid.)

The automatic grid approach will be preferable when the grid contents are uniform and consistent and when re-using semantic elements for grids (typical). The manual approach may be necessary when the grid structure is not uniform or structurally inconsistent (atypical), and involves identifying the parts of the grid on specific focusgroup candidates using CSS.

Elements with the grid focusgroup definition on the root element of the structural grid become automatic grid focusgroups. The implementation must attempt to validate the structure of the grid to ensure it has appropriate row and cell structures. In the event that the implementation cannot automatically determine the grid structure, then the definition is ignored (i.e., there is no fallback to a linear grid).

HTML attribute value	CSS property & value	Explanation
focusgroup="grid"	focus‑group‑name: grid	Establishes the root of an automatic grid focusgroup. Descendants of the automatic grid are identified and assigned `focus-group-item: row` and `focus-group-item: cell` focusgroup candidate status automatically.

Example 22:

<table focusgroup=grid> 
  <tr>…</tr> 
  <tr>…</tr> 
  <tr>…</tr> 
</table>

The <table>'s "grid" focusgroup definition automatically establishes each of its descendant <tr>s as focusgroup candidate rows (the parser-generated <tbody> is accounted for) and <td>s as focusgroup candidate cells. Left/right arrow keys in this grid focusgroup will navigate between cells in the table, and up/down arrow keys will compute the new target based on the DOM position of the current focusgroup candidate cell in relation to the focusgroup candidate row.

6.9.4. Manual grids: row and cell connections

A manual grid is declared in a focusgroup definition with the name manual-grid. With a manual grid, the rows and cells must be explicitly indicated using focus-group-item: row and focus-group-item: cell.

HTML attribute value	CSS property & value	Explanation
n/a	focus‑group‑name: manual-grid	Establishes the root of a manual grid focusgroup. Descendants of the manual grid must be identified with `focus-group-item: row` and `focus-group-item: cell` explicitly.
n/a	focus‑group‑item: row	Must be a descendant of a grid focusgroup root (i.e., the `manual-grid`-named focusgroup element).
n/a	focus‑group‑item: cell	Must be a descendant of a grid focusgroup root (i.e., the `manual-grid`-named focusgroup element). Must also be a descendant of a `focus-group-item: row` focusgroup candidate.

Cells cannot be children of other cells, and rows cannot be children of rows.

Manual grid focusgroup rows and cells do not need to be direct children of the element that includes the manual grid focusgroup definition in order to participate in the grid structure. Each focusgroup candidate will perform an ancestor search to locate its nearest grid structural component: cells will look for their nearest row, and rows will look for their nearest manual-grid root.

In the following example, the <my-cell>s are all meant to be on the same row of the grid, and the rows are designated by <my-row> elements:

Example 23:

<style>
   my-root { focus-group-name: manual-grid; }
   my-row { focus-group-item: row; }
   my-cell { focus-group-name: cell; }
</style>
<!-- ... -->
<my-root>
  <div class="presentational_wrapper">...</div>
  <my-row>
    <first-thing>...</first-thing>
    <cell-container>
      <my-cell>...</my-cell>
      <my-cell>...</my-cell>
    </cell-container>
    <cell-container>
      <my-cell>...</my-cell>
      <my-cell>...</my-cell>
    </cell-container>
  </my-row>
  <!-- repeat pattern of div/my-row pairs... -->
</my-root>

The following non-uniform structure can still have grid semantics added via manual-grid:

Example 24:

<style>
   .root { 
     focus-group-name: manual-grid;
     focus-group-wrap: flow;
   }
   .row { focus-group-item: row; }
   .cell { focus-group-item: cell; }
</style>
<!-- ... -->
<div class="root">
  <div class="row">
    <div>
      <div class="cell"></div>
      <div class="cell"></div>
    </div>
  </div>
  <div>
    <div class="row">
      <div class="cell"></div>
      <div class="cell"></div>
    </div>
  </div>
  <div>
    <div>
      <div class="row">
        <div>
          <div class="cell"></div>
          <div class="cell"></div>
        </div>
      </div>
    </div>
  </div>

6.9.5. Empty Cell data

Like linear focusgroups, focus is only set on elements that are focusable. The arrow key navigation algorithms look for grid focusgroup cells in the direction the arrow was pressed. Non-focusable grid focusgroup candidate cells are passed over in the search.

6.9.6. Non-uniform cells

It is entirely possible to have rows with non-uniform numbers of cells. In these cases, focusgroup navigation behaviors may not work as visibly desired. Algorithms for navigating grid focusgroups will work based on content the grid content structure as specified. If the algorithms conclude that there is not "next candidate cell" to move to (e.g., in a grid with two rows, and the bottom row has three cells, and the top row only two, if the focus is on the 3rd cell, a request to move "up" to the prior row cannot be honored because there is no "3rd cell" in that row.

7. Privacy and Security Considerations

7.1. Privacy

No considerable privacy concerns are expected, but we welcome community feedback.

7.2. Security

No significant security concerns are expected.

8. Alternative Solutions

We considered various alternative solutions before arriving at the current proposal:

We considered a design more closely aligned with HTML's radio button groups, wherein to form a 'focusgroup' each participating element used a similarly-named moniker. The platform was expected to automatically link same-named groups together. This enabled groups to be widely dispersed across the DOM. In practice few scenarios require that degree of flexibility and data locality helps ensure that lists of items stay relatively adjacent to each other structurally. Furthermore, this approach provided no common "controller" element, and additional attributes were proposed to potentially link these groups together. Finally, this proposal suggested that the attribute also enable the element to get keyboard focus if it didn't already have it--another new way of making elements focusable wasn't deemed a great idea.
In another iteration, we considered codifying the ARIA authoring practices applying platform behavior automatically based on the presence of certain ARIA attributes (such as role="tab"). This idea didn't get too far, as we ultimately felt that aria attributes really shouldn't have native behavior locked into them as that sets a bad precedent. It was also considered that aria in some fundamental ways is a patch on top of the native HTML engine for support that should eventually become a native part of the platform. That was the insight that took us in the direction of building a native HTML feature to expose the built-in platform arrow-key navigation of certain controls.

Since at least 2002 the CSS WG has defined related CSS properties nav-up, nav-right, nav-down, nav-left in CSS Basic UI 4's Keyboard Control. These properties are expected to provide focus navigation control similar to focusgroup. They differ in some significant ways:

nav-* are defined using CSS (vs HTML). Not that HTML-without-CSS is really a modern concern, but proposing focusgroup in HTML enables the user agent to setup focusgroups without the CSS dependency (or behavior change should CSS application be delayed due to network conditions).
Each of nav-up, etc., require an explicit content selector (id) for ordering, which makes them relatively brittle. This design presents at least three challenges:
- The possibility of mis-alignment to content. If stylesheet nav-* selectors are not updated in terms of changes to document content (at authoring time) the navigation expectations can get out of sync.
- Unexpected side-effects with responsive design. If the wrapping and reflow of presentational content changes depending on device characteristics (such as orientation, zoom level), authors must likely provide dynamic run-time updates to nav-* properties in order to keep top/left/bottom/right navigation logical per the current layout.
- Related to the previous point, it can be easy to make logical errors in navigation sequences when targeting specific directions. This can lead to directions that don't match the property names (e.g., nav-left actually navigates up or right) while also opening up the possibility of unidirectional navigation (e.g., after navigating right, the user can't go "back" to the left due to missing or erroneous selectors).
Ordering is not based on content. These properties serve visual presentations, but possibly make focus navigation illogical for accessibility users (especially when any element can be targeted by selector).
Verbose descriptors. To get four-direction navigation on one element requires specifying four unique CSS properties.
Special focus handling. The use of a selector on one of the nav-* properties has the unique property of making that element focusable upon keyboard navigation to it. Additional clarity on how this special semantic applies would be needed for implementation. It is unclear (especially given the related Note in the spec) if this is a desirable behavior.

In nearly 20 years, user agents have not implemented these properties. It is likely that focusgroup will create an incongruency in the platform with these nav-* CSS properties. Should the two exist simultaneously, the nav-* properties might provide override semantics for directional movement, and take precedence over the focusgroup attribute. However, we hope that such a conflict will not occur.

Another approach to focusable navigation has been defined in CSS Spatial Navigation. This specification enables user agents to deterministically navigate focusable elements in logical directions (top, left, bottom, and right) according to those element's visual presentation. It assumes that a user agent will use some undefined trigger to enter a "spatial navigation mode" in which the specification-defined behavior will apply. This mechanism of navigating content can be an alternative (or addition to) traditional TAB key navigation (or equivalent) for a variety of devices (like TVs).

Spatial navigation occurs in the context of a "spatial navigation container" which defaults to any scroll container (e.g., the viewport). The specification provides an API to enable programmatic navigation, and offers several CSS properties: to enable additional spatial navigation containers, to control the behavior of focus and scroll actions by navigation keys, and to customize the algorithm used for finding the next focusable element in a given direction.

The specification does not presume to use spatial navigation in a limited (e.g., scoped and grouped) way as focusgroup implies. It appears to assume that arrow key direction navigation will be a primary navigation technique, thus any and all focusable content should participate.

It may be possible for Spatial Navigation and focusgroup to coexist simultaneously in the same content. In the case that spatial navigation is only enabled via a special mode, it would be likely that its navigation model would take precedence over focusgroup, as it is meant to make all visual, focusable content navigable, and would provide a super-set of navigational movement for visual content. It is worth noting that accessibility tools would not likely enable spatial navigation mode.

It seems desirable to have a feature to easily enable spatial-navigation-like behavior for a subset of elements in a presentation. While this would not be ideal for an accessibility-view of the content, it is possible that particular spatial navigation metaphors could be omitted by accessibility tools when performing navigation. For example, when an AT interfaces with the user agent, the AT might limit navigation to "forward/backward" content navigation modes, while a user not working with an AT (or ATs designed for visual navigation) would enable the full spatial navigation model. An opt-in for spatial navigation would certainly be a requirement and could be an extension to focusgroup (e.g., focusgroup=spatial).

10. Open Questions

1. It may not make sense to support focusgroup on every HTML element, especially those that already have platform-provide focusgroup-like internal behavior (e.g., <select>). Then again, if the key navigation behavior is explained by the presence of an external attribute on these elements, perhaps the internal behavior should defer to the external specified behavior (usage of the attribute would cancel the element's preexisting built-in behavior in favor of the new generic behavior). Implementation experience and additional community feedback will be necessary to land a reasonable plan for this case.

10.1. Additional Keyboard support

In addition to arrow keys, the focusgroup should also enable other navigation keys such as pageup/down for paginated movement (TBD on how this could be calculated and in what increments), as well as the home/end keys to jump to the beginning and end of groups.

It might also be interesting to add support for typeahead scenarios (though what values to look for when building an index would need to be worked out, and may ultimately prove to be too complicated).

Acknowledgments

Special thanks to those who have reviewed, commented on, filed issues, and talked with us offline about focusgroup. Your insight and ideas and contributions have helped dramatically improve this proposal.

58 KiB

Исходник Постоянная ссылка Ответственный История

focusgroup for HTML and CSS

Status of this Document

1. Introduction

2. Goal

3. Non-Goals

4. Principles

5. Use Cases

6. Focusgroup Concepts

6.1. Key conflicts

6.2. Key traps

6.3. Enabling wrapping behaviors

6.4. Expanding and connecting linear focusgroups together (`extend`)

6.5. Limiting linear focusgroup directionality

6.6. Interactions with directionality + extending

6.6.1. Axis-aligned extending linear focusgroups

6.6.2. Orthogonal-axis extending linear focusgroups

6.6.3. Notes about wrapping while extending

6.6.4. Deep combinations

6.7. Opting-in & opting-out

6.8. Multiple focusgroups among siblings

6.9. Grid focusgroups

6.9.1. Applicability to tabular data

6.9.2. Grid isolation

6.9.3. Setting up a grid focusgroup

6.9.4. Manual grids: row and cell connections

6.9.5. Empty Cell data

6.9.6. Non-uniform cells

7. Privacy and Security Considerations

7.1. Privacy

7.2. Security

8. Alternative Solutions

9.1. CSS Basic UI 4 Keyboard Navigation properties

9.2. Spatial Navigation

10. Open Questions

10.1. Additional Keyboard support

Acknowledgments

58 KiB Исходник Постоянная ссылка Ответственный История Убрать экранирование Экранировать

focusgroup for HTML and CSS

Status of this Document

1. Introduction

2. Goal

3. Non-Goals

4. Principles

5. Use Cases

6. Focusgroup Concepts

6.1. Key conflicts

6.2. Key traps

6.3. Enabling wrapping behaviors

6.4. Expanding and connecting linear focusgroups together (extend)

6.5. Limiting linear focusgroup directionality

6.6. Interactions with directionality + extending

6.6.1. Axis-aligned extending linear focusgroups

6.6.2. Orthogonal-axis extending linear focusgroups

6.6.3. Notes about wrapping while extending

6.6.4. Deep combinations

6.7. Opting-in & opting-out

6.8. Multiple focusgroups among siblings

6.9. Grid focusgroups

6.9.1. Applicability to tabular data

6.9.2. Grid isolation

6.9.3. Setting up a grid focusgroup

6.9.4. Manual grids: row and cell connections

6.9.5. Empty Cell data

6.9.6. Non-uniform cells

7. Privacy and Security Considerations

7.1. Privacy

7.2. Security

8. Alternative Solutions

9. Related Work

9.1. CSS Basic UI 4 Keyboard Navigation properties

9.2. Spatial Navigation

10. Open Questions

10.1. Additional Keyboard support

Acknowledgments

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6.4. Expanding and connecting linear focusgroups together (`extend`)