PHP Require File statement is identical Include File statement (except upon failure it will also produce a fatal E_COMPILE_ERROR level error).
Also, their syntax relative and absolute file paths are identical.
PHP Require File Statement
require 'myfile.php';
PHP require file from parental directory (folder) - relative path
require(dirname(__DIR__).'/../
myfile.php');
PHP Require File from ROOT directory
require($_SERVER['DOCUMENT_ROOT']."/myfile.php");
PHP Require File deeper directory then ROOT - absolute path
$root = realpath($_SERVER["DOCUMENT_ROOT"]);
require "$root/folder1/folder2/myfile.php";