defsystem optionally loaded subsystem

In one of my systems, I have a few files whose definitions are
infrequently used and that are time-consuming to load.  I would like
to make them optionally load under defsystem-3.x:  they would compile
with the rest of the system, but would only be loaded with an explicit
command.  I do not want to make them a separate system because I want
to keep them associated with this system.  Is there a way to do this
easily in the defsystem structure?

As a side point, I think the documentation is out of date
src/defsystem-3.x/docs/defsystem.html refers to Mark Kantrowitz for
bugs etc.

Liam


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