i installed the xdebug and debgged the file index.php.
This works fine and the breakpoints are all "working". Watches too.

my problem is, that i can't include or add any other file which is NOT located in the same path than the index.php

if i press F7 i step INTO the second file (i found out, that this works, but the file is not opened and so not viewed).

when i open the Call stack, i can see
file:///var/www/inc/file1.inc.php.include:6
index.php {main}:9

/var/www is the root of my apache2 web, this means the Path at the server is correct.
So i think, the debugger can not map /var/www/inc to My Project - Sources.

maybe, this is because i am running the IDE at a windows system and the apache2 at a linux - machine ("/" versus "\")