By now, you should have heard about full site editing, if you have not, you can read all about it here: https://fullsiteediting.com/
Full site editing comes with a lot of changes. But it also lowers the entry barrier for new theme authors. Because they no longer need to be concerned with the Customizer, custom widgets, etc. hence can focus their attention on extending and styling blocks.
Because full site editing themes will contain fewer files, and less CSS, they will be easier to build.
With full site editing, web developers will use HTML templates instead of PHP files and block comments and markup instead of PHP functions.
Theme developers will be able to create and preview layouts by placing blocks in the site editor. When the design is ready, they can now export it as a .zip file with HTML files, directly from the editor’s tools and options modal.
Although the export is not a complete theme, it contains the markup for the blocks, and it can be used as the base for a new theme.
There is a new configuration file called theme.json that both classic themes and block themes can use now. With this file, theme developers will be able to use the JSON format to define defaults for content width, color palettes, background color, text color, padding, and font sizes.
If you also want to set default values for the global styles interface in the editor or create CSS custom properties that can be used for blocks in the editor and the front page, you will have to make use of the file.
However, theme.json isn’t part of the file export from the site editor yet, you’ll need to create it manually.
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