Well, the load rules *are* undocumented apart from the code itself (!)
I was trying to respond to @pelson https://github.com/SciTools/iris/pull/1133#discussion_r12832834 .

I could try to pitch this statement more strongly as a "for completeness" item.
Like.. "This document covers the essentials of the loading process.  The precise details are implemented as follows:"
(so it doesn't actually *say* to go + read the code !)
How does that sound ??