Source

File: wp-includes/widgets/class-wp-widget-media.php

public function sanitize_token_list( $tokens ) {
		if ( is_string( $tokens ) ) {
			$tokens = preg_split( '/\s+/', trim( $tokens ) );
		}
		$tokens = array_map( 'sanitize_html_class', $tokens );
		$tokens = array_filter( $tokens );
		return join( ' ', $tokens );
	}