WordPress at a glance
function is not described

wp_register_custom_classname_support() WP 1.0

Registers the custom classname block attribute for block types that support it.

No Hooks.

Return

null. Nothing.

Usage

wp_register_custom_classname_support( $block_type );
$block_type(WP_Block_Type) (required)
Block Type.

Code of wp_register_custom_classname_support() WP 5.7.2

<?php
function wp_register_custom_classname_support( $block_type ) {
	$has_custom_classname_support = true;
	if ( property_exists( $block_type, 'supports' ) ) {
		$has_custom_classname_support = _wp_array_get( $block_type->supports, array( 'customClassName' ), true );
	}
	if ( $has_custom_classname_support ) {
		if ( ! $block_type->attributes ) {
			$block_type->attributes = array();
		}

		if ( ! array_key_exists( 'className', $block_type->attributes ) ) {
			$block_type->attributes['className'] = array(
				'type' => 'string',
			);
		}
	}
}