Apache Module mod_dir
Summary
    The index of a directory can come from one of two sources:
    
      - A file written by the user, typically called
      index.html. TheDirectoryIndexdirective sets the
      name of this file. This is controlled bymod_dir.
- Otherwise, a listing generated by the server. This is
      provided by mod_autoindex.
The two functions are separated so that you can completely
    remove (or replace) automatic index generation should you want
    to.
 
    A "trailing slash" redirect is issued when the server
    receives a request for a URL
    http://servername/foo/dirname where
    dirname is a directory. Directories require a
    trailing slash, so mod_dir issues a redirect to
    http://servername/foo/dirname/.
    The DirectoryIndex directive sets the
    list of resources to look for, when the client requests an index
    of the directory by specifying a / at the end of the a directory
    name.  Local-url is the (%-encoded) URL of a document on
    the server relative to the requested directory; it is usually the
    name of a file in the directory. Several URLs may be given, in
    which case the server will return the first one that it finds.  If
    none of the resources exist and the Indexes option is
    set, the server will generate its own listing of the
    directory.
    Example
      DirectoryIndex index.html
    
then a request for http://myserver/docs/ would
    return http://myserver/docs/index.html if it
    exists, or would list the directory if it did not.
    Note that the documents do not need to be relative to the
    directory;
    
      DirectoryIndex index.html index.txt  /cgi-bin/index.pl
    
would cause the CGI script /cgi-bin/index.pl to be
    executed if neither index.html or index.txt
    existed in a directory.