content for accessibility tab

src/pages/components/UI-shell-left-panel/accessibility.mdx

@@ -0,0 +1,90 @@
+---
+title: UI shell left panel
+description:
+  This left panel is part of the Carbon UI shell. A shell is a collection of
+  components shared by all products within a platform.
+tabs: ['Usage', 'Style', 'Code', 'Accessibility']
+---
+
+import {
+  StructuredListWrapper,
+  StructuredListHead,
+  StructuredListBody,
+  StructuredListRow,
+  StructuredListInput,
+  StructuredListCell,
+  OrderedList,
+  ListItem,
+} from '@carbon/react';
+
+<PageDescription>
+
+No accessibility annotations are needed for UI shell left panels, but keep these considerations in mind if you are modifying Carbon or creating a custom component.
+
+</PageDescription>
+
+<AnchorLinks>
+
+<AnchorLink>What Carbon provides</AnchorLink>
+<AnchorLink>Development considerations</AnchorLink>
+
+</AnchorLinks>
+
+## What Carbon provides
+
+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.
+
+### Keyboard interaction
+
+The left panel is comprised of both expandable sections (often called "sub-menus") and links to content. All items can be reached by `Tab`. Toggling a collapsed section with `Space` or `Enter` expands it, which reveals additional links. Activating any of the links (with `Enter`) updates the main content area and puts focus back at the top of the page. The link becomes bold to show it is the current page. (It remains in the tab order, but can no longer be activated.)
+
+<Row>
+<Column colLg={8}>
+
+![example of UI shell left panel keyboard interaction](images/left-nav-accessibility-1.png)
+
+<Caption>
+  Sub-menus and links are reached by Tab. Space and Enter keys expand/collapse sub-menus, and the Enter key is used to activate links.
+</Caption>
+
+</Column>
+</Row>
+
+### Non-persistent left panel
+
+On smaller screens, or if content is zoomed up to approximately 175% magnification, Carbon responsively hides the left panel behind a 'hamburger' button, which appears at the start of the UI shell header. Activating the button (with `Space` or `Enter`) causes the left panel to appear. It overlays the main content area, which often becomes dimmed. The hamburger button's icon becomes an X, and must be activated to close the left panel.
+
+<Row>
+<Column colLg={8}>
+
+![hamburger button keyboard interaction](images/left-nav-accessibility-2.png)
+
+<Caption>
+  The hamburger button expands and collapses the left panel.
+</Caption>
+
+</Column>
+</Row>
+
+The left panel can also be implemented as a "Side rail" variant, which slides into view from the left side when reached by keyboard or hovered by mouse. Keyboard interaction within the revealed left panel does not change. When users tab out of the left panel, the side rail slides out of view. 
+<Row>
+<Column colLg={8}>
+
+![the side rail is shown expanding as the user tabs to the left panel location](images/left-nav-accessibility-3.png)
+
+<Caption>
+  The side rail expands on hover or focus, and collapses when not hovered or focused.
+</Caption>
+
+</Column>
+</Row>
+
+## Development considerations
+
+Keep these considerations in mind if you are modifying Carbon or creating a
+custom component.
+
+- the left panel is in a `<nav>` section with `aria-label="Side navigation"`
+- all items in the left panel are in a nested `<ul>` structure, which provides additional information to assistive technologies
+- each 'sub-menu' is implemented as a `<button>` with `aria-expanded`
+- activated links receive an `aria-current="page"` attribute

src/pages/components/UI-shell-left-panel/code.mdx

@@ -3,7 +3,7 @@ title: UI shell left panel
 description:
   This left panel is part of the Carbon UI shell. A shell is a collection of
   components shared by all products within a platform.
-tabs: ['Usage', 'Style', 'Code']
+tabs: ['Usage', 'Style', 'Code', 'Accessibility']
 ---
 
 <PageDescription>

src/pages/components/UI-shell-left-panel/style.mdx

@@ -3,7 +3,7 @@ title: UI shell left panel
 description:
   This left panel is part of the Carbon UI shell. A shell is a collection of
   components shared by all products within a platform.
-tabs: ['Usage', 'Style', 'Code']
+tabs: ['Usage', 'Style', 'Code', 'Accessibility']
 ---
 
 ## Color

src/pages/components/UI-shell-left-panel/usage.mdx

@@ -3,7 +3,7 @@ title: UI shell left panel
 description:
   This left panel is part of the Carbon UI shell. A shell is a collection of
   components shared by all products within a platform.
-tabs: ['Usage', 'Style', 'Code']
+tabs: ['Usage', 'Style', 'Code','Accessibility']
 ---
 
 <PageDescription>