The filesystem module is placed on a Mount point in the name space of the server, e.g. /doc/, and have a search path in the real file system, e.g. /usr/spider/doc/.

The module then tries to map all requests to files, e.g.

/doc/s2.gif -> /usr/spider/doc/s2.gif
/doc/tmp/test.html -> /usr/spider/doc/tmp/test.html
If more than one module have the same mount point, the server will call them in priority order, and the first one that finds a file wins.