I don't completely understand the documentation for the include() function:
"Files for including are first looked in include_path relative to the
current working directory and then in include_path relative to the directory
of current script. E.g. if your include_path is ., current working directory
is /www/, you included include/a.php and there is include "b.php" in that
file, b.php is first looked in /www/ and then in /www/include/. "
How do you know where "the current working directory" is?