Developer Documentation 
Edit
The new editor is highly flexible, like most of WordPress. You can build custom blocks, modify the editor’s appearance, add special plugins, and much more.
Creating Blocks Creating Blocks
The editor is about blocks, and the main extensibility API is the Block API. It allows you to create your own static blocks, Dynamic Blocks ( rendered on the server ) and also blocks capable of saving data to Post Meta for more structured content.
If you want to learn more about block creation, the Blocks Tutorial is the best place to start.
Extending Blocks Extending Blocks
It is also possible to modify the behavior of existing blocks or even remove them completely using filters.
Learn more in the Block Filters section.
Extending the Editor UI Extending the Editor UI
Extending the editor UI can be accomplished with the registerPlugin API, allowing you to define all your plugin’s UI elements in one place.
Refer to the Plugins and Edit Post section for more information.
You can also filter certain aspects of the editor; this is documented on the Editor Filters page.
Meta Boxes Meta Boxes
Porting PHP meta boxes to blocks or sidebar plugins is highly encouraged, learn how through these meta data tutorials.
See how the new editor supports existing Meta Boxes.
Theme Support Theme Support
By default, blocks provide their styles to enable basic support for blocks in themes without any change. Themes can add/override these styles, or rely on defaults.
There are some advanced block features which require opt-in support in the theme. See theme support.
Autocomplete Autocomplete
Autocompleters within blocks may be extended and overridden. Learn more about the autocomplete filters.
Block Parsing and Serialization Block Parsing and Serialization
Posts in the editor move through a couple of different stages between being stored in post_content and appearing in the editor. Since the blocks themselves are data structures that live in memory it takes a parsing and serialization step to transform out from and into the stored format in the database.
Customizing the parser is an advanced topic that you can learn more about in the Extending the Parser section.