The IncludePath option lets you have servlets that can be included or called in servlets using pse.include or pse.call. This list is a comma separated list of directories. Only the directories listed here will be searched.
By default, IncludePath is empty, meaning you cannot include or call external servlets. A typical configuration might include the current directory (.):
IncludePath = .
An example usage would be if all your pages had a common footer. You
could create the file commonfooter.pt and put it in a directory
in IncludePath and then use pse.include('commonfooter.pt')
to include it in every page.