require_once在没有包含路径的情况下工作

Question

I have file 1.php having a require_once for 2.php (both of them are in different folders). The issue I am having is that 1.php seems to magically include 2.php since the path for 2.php is not in 1.php. Just to be sure, I even added a set_include_path('.') before the require_once '2.php', but it still works... Is there something obvious I am missing or is this plain weird??

Edit:

//-- file 1.php
//-- long list of requires...
set_include_path('.');
echo get_include_path();
require_once '2.php';

The above works fine while 1.php and 2.php are in different folders.

Answer 1

There is some include magic in PHP, i've met it before.
Something autoload related, I believe.
It always looks in the folder where file with running class resides