Source

File: wp-includes/class-wp-hook.php

public static function build_preinitialized_hooks( $filters ) {
		/** @var WP_Hook[] $normalized */
		$normalized = array();

		foreach ( $filters as $tag => $callback_groups ) {
			if ( is_object( $callback_groups ) && $callback_groups instanceof WP_Hook ) {
				$normalized[ $tag ] = $callback_groups;
				continue;
			}
			$hook = new WP_Hook();

			// Loop through callback groups.
			foreach ( $callback_groups as $priority => $callbacks ) {

				// Loop through callbacks.
				foreach ( $callbacks as $cb ) {
					$hook->add_filter( $tag, $cb['function'], $priority, $cb['accepted_args'] );
				}
			}
			$normalized[ $tag ] = $hook;
		}
		return $normalized;
	}