6.9.0 RC1

Features

• Support changing the image title attribute in the Image block.

Bugs

• Fix  invalid Pullquote blocks when setting a color from the palette presets.
• Fix the columns left/right full-width margins.
• Prevent fast consecutive updates from triggering blocks reset.
• Fix block movers for floated blocks.
• Fix Radio buttons styling in meta boxes.
• Fix the default image sizes used for featured images displayed in the editor.
• Prevent the unsaved changes warning from popping-up when deleting posts.
• Revert img and iframe styles to block editor container scope.
• Block Merge: guard for undefined attribute definition.

Enhancements

• Inserter: Immediately insert block when only one block type is allowed.
• Update the list of the default available gradients.
• Disable indent/outdent buttons when necessary in the List block.

New APIs

• Add theme support API to define custom gradients presets.
• Mark the AsyncMode data module API as stable.
• Mark the mediaUpload @wordpress/block-editor setting as stable.
• Add a wpenv.json config file support for @wordpress/env.

Various

• Refactor the way HTML is escaped by the RichText component.
• Refactor and simplify the block margins CSS in the editor.
• Use HTTPS git clone in the Gutenberg release tool for more stability.
• Update ExternalLink, BaseControl and FormTokenField components to use the VisuallyHidden component for the screen reader text.
• Add several components to Storybook: 
  • Spinner,
  • Draggable,
  • RangeControl,
  • FontSizePicker,
  • Modal,
  • Snackbar,
  • ToggleControl,
  • ResizableBox.
• Refactor the block-directory search to insert as an Inserter plugin.
• Improve the experimental useColors React hook.
• Upgrade Puppeteer to the last version.
• Update to the last version of npm-package-json-lint.
• i18n: Fix string concatenation in the Verse block example and add translators string.
• Change Detection: Add an e2e test case for post trashing.
• Fix the e2e tests watch command.

Experimental

• Block Content Areas:
  • Support loading block templates from themes.
• Navigation block:
  • Add default frontend styles for the Navigation block.
  • Use RichText for navigation menu item instead of TextControl.
  • Add block navigator to the inspector panel.
  • Use an SVG icon for the color selector.
  • Add a new API for horizontal movers and use it for the navigation block.
  • Add a new Link creation and edition UI and use it for the navigation block.
  • Add an appender to the block navigator.
  • Add a block placeholder.
  • Various fixes and refactorings: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15.
• Add ResponsiveBlockControl component.
• Add initial API for block patterns.

Documentation

• Add an introduction README for Storybook.
• Typos and fixes: 1, 2, 3, 4, 5, 6.