Source

File: wp-includes/Requests/Transport/fsockopen.php

protected static function accept_encoding() {
		$type = array();
		if (function_exists('gzinflate')) {
			$type[] = 'deflate;q=1.0';
		}

		if (function_exists('gzuncompress')) {
			$type[] = 'compress;q=0.5';
		}

		$type[] = 'gzip;q=0.5';

		return implode(', ', $type);
	}