WordPress at a glance
function is not described

wp_apply_custom_classname_support() WP 1.0

Add the custom classnames to the output.

No Hooks.

Return

Array. Block CSS classes and inline styles.

Usage

wp_apply_custom_classname_support( $block_type, $block_attributes );
$block_type(WP_Block_Type) (required)
Block Type.
$block_attributes(array) (required)
Block attributes.

Code of wp_apply_custom_classname_support() WP 5.7.2

<?php
function wp_apply_custom_classname_support( $block_type, $block_attributes ) {
	$has_custom_classname_support = true;
	$attributes                   = array();
	if ( property_exists( $block_type, 'supports' ) ) {
		$has_custom_classname_support = _wp_array_get( $block_type->supports, array( 'customClassName' ), true );
	}
	if ( $has_custom_classname_support ) {
		$has_custom_classnames = array_key_exists( 'className', $block_attributes );

		if ( $has_custom_classnames ) {
			$attributes['class'] = $block_attributes['className'];
		}
	}

	return $attributes;
}