acf/pre_load_attachment хук-фильтр . ACF 1.0

Allow filter to short-circuit load attachment logic. Alternatively, this filter may be used to switch blogs for multisite media functionality.

Использование

add_filter( 'acf/pre_load_attachment', 'filter_function_name_9255', 10, 2 );
function filter_function_name_9255( $null, $attachment ){
	// filter...

	return $null;
}

$null

-

$attachment

-

Где вызывается хук

$response = apply_filters( "acf/pre_load_attachment", null, $attachment );

Где используется хук в ядре Advanced Custom Fields