Source

File: wp-includes/formatting.php

function wp_spaces_regexp() {
	static $spaces = '';

	if ( empty( $spaces ) ) {
		/**
		 * Filters the regexp for common whitespace characters.
		 *
		 * This string is substituted for the \s sequence as needed in regular
		 * expressions. For websites not written in English, different characters
		 * may represent whitespace. For websites not encoded in UTF-8, the 0xC2 0xA0
		 * sequence may not be in use.
		 *
		 * @since 4.0.0
		 *
		 * @param string $spaces Regexp pattern for matching common whitespace characters.
		 */
		$spaces = apply_filters( 'wp_spaces_regexp', '[\r\n\t ]|\xC2\xA0| ' );
	}

	return $spaces;
}