<?php
/**
 * Block Name: Hero
 * Description: Displays a full width hero image with text overlay
 */

// $data is what we're going to expose to our render template
$data = array(
    'example_field' => get_field( 'example_field' ),
    'another_field' => get_field( 'another_field' )
);

// Dynamic block ID
$block_id = 'hero-' . $block['id'];

// Check if a custom ID is set in the block editor
if( !empty($block['anchor']) ) {
    $block_id = $block['anchor'];
}

// Block classes
$class_name = 'hero-block';
if( !empty($block['class_name']) ) {
    $class_name .= ' ' . $block['className'];
}

/** 
 * Pass the block data into the template part
 */ 
get_template_part(
    'theme/blocks/hero/render',
    null,
    array(
        'block'      => $block,
        'is_preview' => $is_preview,
        'post_id'    => $post_id,

        'data'       => $data,
        'class_name' => $class_name,
        'block_id'   => $block_id,
    )
);

{
    "name": "hero",
    "title": "Hero",
    "description": "Displays a full width hero image with text overlay",
    "category": "theme",
    "apiVersion": 2,
    "acf": {
        "mode": "preview",
        "renderTemplate": "theme/blocks/hero/block.php"
    },
    "supports": {
        "anchor": true,
        "jsx": true
    }
}

<?php
/**
 * Block Name: Hero
 * Description: Displays a full width hero image with text overlay
 */

// The block attributes
$block = $args['block'];

// The block data
$data = $args['data'];

// The block ID
$block_id = $args['block_id'];

// The block class names
$class_name = $args['class_name'];

$template = array(
    array('core/heading', array(
        'level' => 2,
        'content' => 'This is a default heading',
    )),
    array( 'core/paragraph', array(
        'content' => 'This is placeholder paragraph text.',
    ) )
);

$allowed_blocks = array( 'core/heading', 'core/paragraph', 'core/image' );
?>

<div id="<?php echo $block_id; ?>" class="<?php echo $className; ?>">
    <InnerBlocks 
        template="<?php echo esc_attr( wp_json_encode( $template ) ); ?>"
        allowedBlocks="<?php echo esc_attr( wp_json_encode( $allowed_blocks ) ); ?>"/>
</div>

<?php
function create_acf_block_cli_register_blocks() {
    // ACF Block Registration
    $blocks=array();
    foreach ($blocks as $block) {
        register_block_type( get_template_directory() . '/blocks/' . $block );
    }
}
add_action( 'init', 'create_acf_block_cli_register_blocks' );