Source

File: wp-includes/pluggable.php

function wp_sanitize_redirect( $location ) {
		// Encode spaces.
		$location = str_replace( ' ', '%20', $location );

		$regex    = '/
		(
			(?: [\xC2-\xDF][\x80-\xBF]        # double-byte sequences   110xxxxx 10xxxxxx
			|   \xE0[\xA0-\xBF][\x80-\xBF]    # triple-byte sequences   1110xxxx 10xxxxxx * 2
			|   [\xE1-\xEC][\x80-\xBF]{2}
			|   \xED[\x80-\x9F][\x80-\xBF]
			|   [\xEE-\xEF][\x80-\xBF]{2}
			|   \xF0[\x90-\xBF][\x80-\xBF]{2} # four-byte sequences   11110xxx 10xxxxxx * 3
			|   [\xF1-\xF3][\x80-\xBF]{3}
			|   \xF4[\x80-\x8F][\x80-\xBF]{2}
		){1,40}                              # ...one or more times
		)/x';
		$location = preg_replace_callback( $regex, '_wp_sanitize_utf8_in_redirect', $location );
		$location = preg_replace( '|[^a-z0-9-~+_.?#=&;,/:%!*\[\]()@]|i', '', $location );
		$location = wp_kses_no_null( $location );

		// Remove %0D and %0A from location.
		$strip = array( '%0d', '%0a', '%0D', '%0A' );
		return _deep_replace( $strip, $location );
	}