wp_allowed_protocols() │ WP 3.3.0

Retrieves a list of protocols to allow in HTML attributes.

Hooks from the function

Return

String[]. Array of allowed protocols. This covers all common link protocols, except for 'javascript' which should not be allowed for untrusted users.

Usage

wp_allowed_protocols();

Notes

Changelog

Since 3.3.0 Introduced.
Since 4.3.0 Added 'webcal' to the protocols array.
Since 4.7.0 Added 'urn' to the protocols array.
Since 5.3.0 Added 'sms' to the protocols array.
Since 5.6.0 Added 'irc6' and 'ircs' to the protocols array.

wp_allowed_protocols() code WP 6.5.2

wp-includes/functions.php 
function wp_allowed_protocols() {
	static $protocols = array();

	if ( empty( $protocols ) ) {
		$protocols = array( 'http', 'https', 'ftp', 'ftps', 'mailto', 'news', 'irc', 'irc6', 'ircs', 'gopher', 'nntp', 'feed', 'telnet', 'mms', 'rtsp', 'sms', 'svn', 'tel', 'fax', 'xmpp', 'webcal', 'urn' );
	}

	if ( ! did_action( 'wp_loaded' ) ) {
		/**
		 * Filters the list of protocols allowed in HTML attributes.
		 *
		 * @since 3.0.0
		 *
		 * @param string[] $protocols Array of allowed protocols e.g. 'http', 'ftp', 'tel', and more.
		 */
		$protocols = array_unique( (array) apply_filters( 'kses_allowed_protocols', $protocols ) );
	}

	return $protocols;
}