Content switcher accessibility (#3375)

* Update accessibility.mdx

update text on the accessibility tab

* new images and alt text

* Update accessibility.mdx

lightened language

* Update accessibility.mdx

minor updates to dev considerations

* Update accessibility.mdx

updates to make the interaction clearer

* lauren's image updates

src/pages/components/content-switcher/accessibility.mdx

@@ -2,7 +2,7 @@
 title: Content switcher
 description:
   Content switchers manipulate the content shown following an exclusive or
-  “either/or” pattern. It is used to toggle between two or more content sections
+  "either/or" pattern. It is used to toggle between two or more content sections
   within the same space on screen.
 tabs: ['Usage', 'Style', 'Code', 'Accessibility']
 ---
@@ -20,83 +20,104 @@ import {
 
 <PageDescription>
 
-The content switcher React Carbon component has been tested against the latest
-[W3C Web Content Accessibility Guidelines (WCAG) 2.1 Level A and AA success criteria](https://www.w3.org/TR/WCAG21/)
-and violations have been identified as high priority issues. This document will
-be updated when these accessibility issues are resolved.
+Design annotations are needed for specific instances shown below, but for the
+standard content switcher component, Carbon already incorporates accessibility.
 
 </PageDescription>
 
 <AnchorLinks>
-  <AnchorLink>Accessibility considerations</AnchorLink>
-  <AnchorLink>Resources</AnchorLink>
-  <AnchorLink>Accessibility testing</AnchorLink>
+  <AnchorLink>What Carbon provides</AnchorLink>
+  <AnchorLink>Design recommendations</AnchorLink>
+  <AnchorLink>Development considerations</AnchorLink>
 </AnchorLinks>
 
-## Accessibility considerations
+## What Carbon provides
 
-1. Each content switcher tab must have a unique title that clearly describes the
-   content panel. This is particularly helpful for users of assistive
-   technologies so they have the necessary information to efficiently navigate
-   the content.
-2. Carbon components should be used to create the content that displays within
-   each content panel.
-3. Content authors need to ensure the content that is added to the tab panel is
-   accessible. For example, if you add an image to the panel you need to include
-   alternative text to pass accessibility testing.
+Carbon bakes keyboard operation into its components, improving the experience of
+blind users and others who operate via the keyboard. Carbon incorporates many
+other accessibility considerations, some of which are described below.
 
-## Resources
+### Keyboard interactions
 
-- [W3C WAI-ARIA Tab Design Pattern](https://www.w3.org/TR/wai-aria-practices-1.1/#tabpanel)
-  covers the usage of ARIA names, state and roles, as well as the expected
-  keyboard interactions.
-- [IBM Accessibility Requirements](https://www.ibm.com/able/requirements/requirements/):
+Like tabs, content switchers can be automatic or manual. In both instances, the
+content switcher takes one tab stop, and arrow keys are used to navigate between
+content tabs.
 
-  - [1.3.1 Info and Relationships](https://www.ibm.com/able/requirements/requirements/#1_3_1)
-    (WCAG Success Criteria
-    [1.3.1](https://www.w3.org/WAI/WCAG21/Understanding/info-and-relationships))
-  - [1.3.2 Meaningful Sequence](https://www.ibm.com/able/requirements/requirements/#1_3_2)
-    (WCAG Success Criteria
-    [1.3.2](https://www.w3.org/WAI/WCAG21/Understanding/meaningful-sequence))
+<Row>
+<Column colLg={8}>
+
+![A user tabs to the content switcher then changes the selection with left and right arrow keys. Pressing tab again moves focus to a link inside the section's content.](images/content-switcher-accessibility-1.png)
+
+<Caption>
+  Manual and automatic content switchers have the same basic keyboard
+  interaction.
+</Caption>
+
+</Column>
+</Row>
+
+Automatic and manual switchers differ in how they are activated. The following
+illustration shows what will happen for each variant when a right arrow key is
+pressed with the All content tab selected and focused.
+
+For automatic switchers, focus and selection are synchronized. When the user
+arrows to a tab, it is selected and the content section under the switcher is
+updated in real time.
+
+Manual switchers allow the user to arrow between the content tabs without
+updating the content section underneath. When the user right arrows, the All
+content tab remains selected while focus moves to the Read tab. In order to
+select the Read tab (and update the content section under the switcher) the user
+would press `Enter` or `Space`.
+
+<Row>
+<Column colLg={8}>
 
-## Accessibility testing
+![Two variants of a content switcher with tabs called All, Read and Unread. In the first, the Read tab is selected and focused. In the second the All tab is selected and the Read tab has a focus indicator](images/content-switcher-accessibility-2.png)
 
-Automated, manual and screen reader accessibility verification test has been
-performed on the Content Switcher React Carbon Component.
-[WCAG 2.1 Level A and AA success criteria](https://www.w3.org/TR/WCAG21/) issues
-have been identified and the list of open accessibility violations is available
-in the Carbon Component GitHub repository.
+<Caption>
+  Arrows keys alone update the selected tab in an automatic content switcher.
+  The Space and Enter keys are used to select a content tab after arrowing to it
+  in a manual variant.
+</Caption>
 
-### Automated test
+</Column>
+</Row>
+
+## Design recommendations
+
+### Indicate which variant to implement
+
+The automatic and manual switchers are visually indistinguishable in a
+wireframe, so designers should annotate which variant the team has decided to
+implement. Since the choice largely concerns technical considerations about
+potential latency when updating the content section’s information, architects or
+developers should be involved in the discussion.
 
 <Row>
-  <Column noGutterSm>
-    <StructuredListWrapper>
-      <StructuredListHead>
-        <StructuredListRow head>
-          <StructuredListCell head>
-            Automated test environment
-          </StructuredListCell>
-          <StructuredListCell head>Results</StructuredListCell>
-        </StructuredListRow>
-      </StructuredListHead>
-      <StructuredListBody>
-        <StructuredListRow>
-          <StructuredListCell>
-            - macOS Mojave version 10.14.2 with VoiceOver
-            <br />
-            - Chrome version 77.0.3865.90
-            <br />
-            - Dynamic Assessment Plugin (DAP) version 1.8.0.0 - IBM
-            Accessibility WCAG 2.1 Sept. 2019 Ruleset
-            <br />- Carbon React version 7.7.1
-          </StructuredListCell>
-          <StructuredListCell>
-            <strong>DAP test:</strong>
-            <br />- Violations
-          </StructuredListCell>
-        </StructuredListRow>
-      </StructuredListBody>
-    </StructuredListWrapper>
-  </Column>
+<Column colLg={8}>
+
+![Two content switchers, one with a pink annotation reading "auto", the other with an annotation "manual"](images/content-switcher-accessibility-3.png)
+
+<Caption>
+  Annotate whether the switcher should be implemented as automatic or manual.
+</Caption>
+
+</Column>
 </Row>
+
+## Development considerations
+
+Keep these considerations in mind if you are modifying Carbon or creating a
+custom component.
+
+- The Content switcher is implemented as a `tablist`, with each content tab
+  implemented as a `<button>` with a role of `tab`.
+- The selected content tab has attributes `aria-selected="true"` and
+  `tabindex="0"`. All other tabs have these attribute values set to `"false"`
+  and `"-1"`.
+- See the
+  [ARIA authoring practices guidance for tabs](https://w3c.github.io/aria-practices/#tabpanel)
+  for more considerations.
+- For accessibility considerations for manual content switchers, see
+  [Deciding when to make selection automatically follow focus](https://w3c.github.io/aria-practices/#kbd_selection_follows_focus).