The support provided for layered software is essentially the same as that
provided for maintaining the core system itself. Each "external package"
(in most cases this actually refers to a tree of packages) is a system in
itself, similar in structure to the core IRAF system. Hence, there is a
LIB, one or more BINs, a HELP database, and all the sources and runtime
files. A good example of an external package is the NOAO package. Except
for the fact that NOAO happens to be located in the IRAF root directory,
NOAO is equivalent to any other layered product, e.g., STSDAS, PROS,
CTIOLOCAL, KPNOLOCAL, etc. Other layered products should be rooted
somewhere outside the [IRAF] directory tree to simplify updates.