This tells smarty to respect the include_path
within the File Template Resource handler and the plugin loader
to resolve the directories known to $template_dir.
The flag also makes the plugin loader check the include_path for
$plugins_dir.
Note
You should not design your applications to rely on the include_path, as this may - depending on your implementation - slow down your system (and Smarty) considerably.
If use_include_path is enabled, file discovery for
$template_dir and
$plugins_dir
work as follows.
For each element
$directoryin array ($template_dir or $plugins_dir) doTest if requested file is in
$directoryrelative to the current working directory. If file found, return it.For each
$pathin include_path doTest if requested file is in
$directoryrelative to the$path(possibly relative to the current working directory). If file found, return it.Try default_handler or fail.
This means that whenever a directory/file relative to the current working directory is encountered, it is preferred over anything potentially accessible through the include_path.
Note
Smarty does not filter elements of the include_path. That means a ".:" within your include path will trigger the current working directory lookup twice.
See also
Template Resources and
$template_dir