what are the acceptable layouts of a yum repository?

   one last question for the day. i was experimenting with
creating a local yum repository on fedora 19 following along
here:

http://www.unixmen.com/setup-local-yum-repository-in-fedora-19/

and it seemed to work fine, but the resulting structure was
simpler than i was used to -- the end result was (in my case)
a new repository under /usr/local/repo in which the rpm files
were right at the top level, along with the repodata/ directory.

   from my previous usage of fedora repos, i'm used to having a
top-level repodata/ directory, along with a Packages/ directory,
which is further broken down based on the first letter of the
package name.

   so what are the valid variations that will be (automatically?)
recognized by yum? i'm guessing the top-level repodata/ directory
is mandatory but, beyond that, what kind of variations can be
used to store the rpm files? thanks.

rday