Currently all include()-type functions with relative include paths are relative to file, which is server by webserver ($SCRIPT_NAME).

It would make life a lot easier if include() could be enchanced to accept optional flag parameter (or perhaps it would be better to create new function names to avoid magic-flag -pollution).

And if it's set, include would be done relative to including file (instead of $SCRIPT_NAME).

For example with this ability, following code should work as expected:

index.php (also $SCRIPT_NAME):
<?php include("include/second.php"); ?>

include/second.php:
<?php include("third.php",1); ?>

include/third.php:
<?php echo "Ok."; ?>

This allows much easier code portability where directory trees are different (difficult to play with $DOCUMENT_ROOT).