How to register block variations with PHP in WP 6.5

[justintadlock]

WordPress 6.5 is shipping with a new get_block_type_variations filter hook: https://github.com/WordPress/wordpress-develop/blob/4ba0963a1f61d062d7345e429c823f3eb5ab5f78/src/wp-includes/class-wp-block-type.php#L608-L616

This essentially works as a PHP-based method of registering custom block variations. This would be a lightweight tutorial for anyone who wants to pick it up and showcase a new WP 6.5 feature. Of course, I'm always happy to take this one on myself too.

Some possible limitations I've seen in my early testing so far:

• It doesn't seem that you can pass a custom SVG to the icon property. I believe this may only be limited to dashicons.
• The isActive check seems to be limited to the array method of checking attributes.

Example

Here's an example variation on the Spacer block that's specific to my theme, but it's just a PoC:

add_filter('get_block_type_variations', function($variations, $block_type) {

	if ('core/spacer' === $block_type->name) {
		$variations[] = [
			'name'       =>      'x3p0/theme-spacer',
			'title'      =>      __('Spacer', 'x3p0-ideas'),
			'keywords'   =>   [ 'space', 'spacer', 'spacing' ],
			'isDefault'  => true,
			'isActive'   => [ 'height' ],
			'attributes' => [
				'height' => 'var:preset|spacing|plus-8'
			]
		];
	}

	return $variations;
});