WordPress Theme developers are probably already familiar with Classic PHP Themes. But there's a new kid on the block, Block Themes (sorry, no pun intended 😏).
Benefits of Block Themes
Block themes improve scalability and performance.
In a standard HTML file, you would include an HTML tag,
In block themes, these HTML elements are added for you. Necessary PHP hooks that you would add to a classic theme, including
wp_footer(), are also added automatically. The markup that is inside the template file is printed between the opening and closing body tags.
Differences & Similarities between Classic PHP Themes & Block Themes (see chart below).
What is a Theme JSON?
Theme.json is a configuration file for theme styles and block settings. Theme.json can be added to ANY theme. It works with both classic PHP-based themes as well as block themes. However Theme.json does not work with the classic editor.
Creating New Themes with Full Site Editing (FSE only works with Block Themes)
Block Themes may not be everyone's cup of tea so WordPress will continue supporting Classic PHP Themes. But if you're looking for full site editing, faster performance or a streamlined site without baked-in widgets, Block Themes could be your golden ticket.
Astra - https://wpastra.com/
Ultra - https://themify.me/themes/ultra/
yes .. WP is .json