This release includes significant progress in consolidating the codebase and refining aspects of the experience. Notably, it introduces APIs for extending Gutenberg beyond blocks, allowing plugins to register a full sidebar for their functionality. There are also expansions to the template support (now allows to declare nested structures), ability to duplicate blocks, various design adjustments, etc. Overall the tone has been fine tuning existing elements and simplifying implementations.

2.3 🍇

• Continue editing flow iterations by adding a line between blocks to insert new content — it also works within nested groups.
• Add support for nested templates.
• Allow duplicating a block through a menu button.
• Automatically set a matching block as the default when a post format is set and the post is empty. This continues the path of matching blocks with post formats.
• Add CodeMirror (core library) to the HTML block for syntax highlighting.
• Simplify design presentation of editor header area for better consistency. (Add label for "Preview" action.)
  
• Introduce new API for allowing plugins to register sidebars. ⭐️  It allows plugins to further extend Gutenberg natively with non-content functionality. Note: the public facing functions are marked as experimental as they are being iterated in the context of the major extensibility work going on outside of blocks.

Other Changes

• Improve the "invalid block" dialog by reducing the options and adding a new convert to blocks feature as we have solidified the transformations.
• Allow adding images to a gallery without going through the media library.
• Show the block appender even if the last block is non empty paragraph.
• Show the side inserter on empty paragraphs within nested blocks.
• Add a script that creates a PHP file based on a POT to make the plugin translatable.
• Refactor float alignment to avoid margin calculations and simplify rendering.
  
• Support registering and invoking actions in the data module.
• Add hook to validate useOnce blocks.
• Add viewport module. (Showing explorations with data module.)
• Provide a fix for apiRequest in sites configured to use plain permalinks. (Reported several times!)
• Remove specific grammar support for more tag as we consolidate the syntax and reduce weight.
• Move filter for registering block types before validation happens.
• Allow removing the selected image in a gallery block using backspace/delete keys.
• Make saved blocks preview available to keyboard users.
• Refactor reducer enhancers as higher-order reducer creators.
• Refactor query HOC usage with withSelect.
• Refactor API calls in Gutenberg to always use wp.apiRequest.
• Register core blocks on init hook.
• Removed DefaultBlockAppender when a template Lock exits.
• Reduce and simplify float code.
• Refactor and cleanup for the Ellipsis and More Menu components.
• Add focus styles for Windows High Contrast mode.
• Move meta boxes out of the generic editor module.
• Make the "more" tag visible in the Classic block.
• Expose ImagePlaceholder component in wp.blocks.
• Rename TermTreeSelect to TreeSelect and move it to components.
• Reuse isHorizontalEdge for RichText component and remove duplication.
• Improve CSS for gallery caption and avoid UI shifts.
• Use TreeSelect in HierarchicalTermSelector.
• Flatten components modes directory organization.
• Mutate editor store reference in middlewares application.
• Consider term names as case insensitive.
• Resolve an issue where removing a block which had contained inner blocks would not clear those inner blocks from state.
• Make sure block usage is incremented (for calculating frequency and recency) when adding blocks with the side inserter.
• Hide non editor specific notices, pending further improvements.
• Update shortcode block icon.
• Disable post format input if the theme does not support post formats.
• Remove margin from initial insertion point and fix misalignment.
• Polish header for mobile and accommodate other more languages.
• Improve handling of block toolbar on mobile.
• Show taxonomies in the document inspector separately, uncoupling Categories & Tags.
• Fix issue with gallery images not cropping within link wrappers.
• Fix bug in paragraph blocks affecting input behaviour when block is positioned on left or right.
• Fix minor inconsistency with block margins and the default appender.
• Fix description typo in freeform block.
• Fix issue with focus transfering between citation and content.
• Fix issue with floated block toolbar on adjacent floats.
• Fix duplicate upload of media on drag.
• Fix issue that prevented adding new rows or columns in Table block.
• Fix issues with z-index and the sidebar.
• Fix accessibility issues with mover icons.
• Fix issue with default block replace resulting in incorrect order.
• Fix sidebar tab padding.
• Fix certain conflicts with markdown plugins.
• Fix IconButton indent regression.
• Fix issue with self embedding WP posts and the processing of the embed markup.
• Fix extraction of _nx translation function.
• Fix wp.data.query backwards compatibility with props.
• Fix problem with delete key in empty contentEditables.
• Resolve an issue with the data module's unsubscribe behavior which can result in a listener callback being invoked even after its been unsubscribed.
• Remove the api-request JavaScript shim which had existed while WordPress 4.9 was in pre-release.
• Remove explicit handling of "bottom reached" within writing flow as redundant.
• Remove invalid reference to WeakMap polyfill.
• Remove unused wpautop fixture files.
• Remove non-functional custom taxonomies meta boxes.
• Remove is- prefix from embed alignment class.
• Switch get_locale() to get_user_locale().
• Remove unnecessary $current_screen code.
• Reduce duplication in 'No saved blocks' and 'No blocks found' component messages.
• Include string extraction in production build.
• Add deprecation helper functions for consistent messaging.
• Improve string cast render test.
• Add Gutenberg svg to docs.
• Add documentation describing block transforms.
• Add documentation for nested template definitions.
• Add documentation for registering sidebar APIs. Move them to extensibility docs.
• Update WordPress packages to the latest versions.