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function is not described

_deprecated_hook() WP 4.6.0

Marks a deprecated action or filter hook as deprecated and throws a notice.

Use the deprecated_hook_run action to get the backtrace describing where the deprecated hook was called.

Default behavior is to trigger a user error if WP_DEBUG is true.

This function is called by the do_action_deprecated() and apply_filters_deprecated() functions, and so generally does not need to be called directly.

This is an internal function for using it by WP core itself. It's not recommended to use this function in your code.

Return

null. Nothing.

Usage

_deprecated_hook( $hook, $version, $replacement, $message );
$hook(string) (required)
The hook that was used.
$version(string) (required)
The version of WordPress that deprecated the hook.
$replacement(string)
The hook that should have been used.
Default: ''
$message(string)
A message regarding the change.
Default: ''

Changelog

Since 4.6.0 Introduced.
Since 5.4.0 The error type is now classified as E_USER_DEPRECATED (used to default to E_USER_NOTICE).

Code of _deprecated_hook() WP 5.7.2

<?php
function _deprecated_hook( $hook, $version, $replacement = '', $message = '' ) {
	/**
	 * Fires when a deprecated hook is called.
	 *
	 * @since 4.6.0
	 *
	 * @param string $hook        The hook that was called.
	 * @param string $replacement The hook that should be used as a replacement.
	 * @param string $version     The version of WordPress that deprecated the argument used.
	 * @param string $message     A message regarding the change.
	 */
	do_action( 'deprecated_hook_run', $hook, $replacement, $version, $message );

	/**
	 * Filters whether to trigger deprecated hook errors.
	 *
	 * @since 4.6.0
	 *
	 * @param bool $trigger Whether to trigger deprecated hook errors. Requires
	 *                      `WP_DEBUG` to be defined true.
	 */
	if ( WP_DEBUG && apply_filters( 'deprecated_hook_trigger_error', true ) ) {
		$message = empty( $message ) ? '' : ' ' . $message;

		if ( $replacement ) {
			trigger_error(
				sprintf(
					/* translators: 1: WordPress hook name, 2: Version number, 3: Alternative hook name. */
					__( '%1$s is <strong>deprecated</strong> since version %2$s! Use %3$s instead.' ),
					$hook,
					$version,
					$replacement
				) . $message,
				E_USER_DEPRECATED
			);
		} else {
			trigger_error(
				sprintf(
					/* translators: 1: WordPress hook name, 2: Version number. */
					__( '%1$s is <strong>deprecated</strong> since version %2$s with no alternative available.' ),
					$hook,
					$version
				) . $message,
				E_USER_DEPRECATED
			);
		}
	}
}