WordPress: Usage of Block Bindings API for custom fields

book-author.html

<!-- wp:paragraph {
	"metadata":{
		"bindings":{
			"content":{
				"source":"core/post-meta",
				"args":{
					"key":"book-author"
				}
			}
		}
	}
} -->
<p></p>
<!-- /wp:paragraph --

book-genre.html

<!-- wp:paragraph {
	"metadata":{
		"bindings":{
			"content":{
				"source":"core/post-meta",
				"args":{
					"key":"book-genre"
				}
			}
		}
	}
} -->
<p></p>
<!-- /wp:paragraph -->

functions.php

<?php

add_action( 'init', function () {

register_meta(
    'post',
    'book-genre',
    [
        'show_in_rest' => true,
        'single'       => true,
        'type'         => 'string',
        'default'      => 'Default text field',
    ]
);

register_meta(
    'post',
    'book-author',
    [
        'show_in_rest' => true,
        'single'       => true,
        'type'         => 'string',
        'default'      => 'Default text field',
    ]
);


} );

synced-pattern-with-overrides.html

<!-- wp:columns -->
<div class="wp-block-columns"><!-- wp:column {"width":"100%"} -->
<div class="wp-block-column" style="flex-basis:100%"><!-- wp:paragraph {"metadata":{"bindings":{"content":{"source":"core/post-meta","args":{"key":"book-genre"}},"__default":{"source":"core/pattern-overrides"}},"name":"Genre"}} -->
<p></p>
<!-- /wp:paragraph --></div>
<!-- /wp:column -->

<!-- wp:column -->
<div class="wp-block-column"><!-- wp:paragraph {"metadata":{"bindings":{"content":{"source":"core/post-meta","args":{"key":"book-author"}},"__default":{"source":"core/pattern-overrides"}},"name":"Author"}} -->
<p></p>
<!-- /wp:paragraph --></div>
<!-- /wp:column --></div>
<!-- /wp:columns -->

Other resources (Japanese):

• https://youtu.be/V0eIcxWhdDM
• https://wordpress.dyno.design/block-bindings-api-custom-field-edit/