Add screen reader instructions for navigating child blocks on block selection

packages/block-editor/src/components/block-list/use-block-props/index.js

@@ -33,6 +33,7 @@ import { useEventHandlers } from './use-selected-block-event-handlers';
 import { useNavModeExit } from './use-nav-mode-exit';
 import { useBlockRefProvider } from './use-block-refs';
 import { useIntersectionObserver } from './use-intersection-observer';
+import { useBlockScreenReaderDescription } from './use-block-screen-reader-description';
 import { store as blockEditorStore } from '../../../store';
 
 /**
@@ -148,6 +149,7 @@ export function useBlockProps(
 		tabIndex: 0,
 		role: 'document',
 		'aria-label': blockLabel,
+		'aria-description': useBlockScreenReaderDescription( clientId ),
 		'data-block': clientId,
 		'data-type': name,
 		'data-title': blockTitle,

packages/block-editor/src/components/block-list/use-block-props/use-block-screen-reader-description.js

@@ -0,0 +1,57 @@
+/**
+ * WordPress dependencies
+ */
+import { sprintf, __ } from '@wordpress/i18n';
+import { getBlockType } from '@wordpress/blocks';
+import { useSelect } from '@wordpress/data';
+/**
+ * Internal dependencies
+ */
+import { store as blockEditorStore } from '../../../store';
+
+export function useBlockScreenReaderDescription( clientId ) {
+	const { hasChildBlocks, blockTitle, canSupportChildBlocks } = useSelect(
+		( select ) => {
+			const {
+				getBlockRootClientId,
+				getBlockName,
+				getBlock,
+				getBlockListSettings,
+			} = select( blockEditorStore );
+			const clientIdToUse = getBlockRootClientId( clientId );
+			const blockName = getBlockName(
+				clientIdToUse ? clientIdToUse : clientId
+			);
+			const blockType = getBlockType( blockName );
+			return {
+				hasChildBlocks:
+					getBlock( clientIdToUse ? clientIdToUse : clientId )
+						?.innerBlocks?.length > 0,
+				blockTitle: blockType?.title,
+				canSupportChildBlocks: getBlockListSettings(
+					clientIdToUse ? clientIdToUse : clientId
+				),
+			};
+		},
+		[ clientId ]
+	);
+	let description;
+	if ( canSupportChildBlocks ) {
+		if ( hasChildBlocks ) {
+			description = sprintf(
+				// Translators: 1: The block title to lowercase for good sentence structure.
+				__( 'Press Escape key to navigate child blocks of %1$s.' ),
+				blockTitle.toLowerCase()
+			);
+		} else {
+			description = sprintf(
+				// Translators: 1: The block title to lowercase for good sentence structure.
+				__(
+					'Press Tab followed by Enter keys to add a child block to %s.'
+				),
+				blockTitle.toLowerCase()
+			);
+		}
+	}
+	return description;
+}