line-map.c

[Robert Dewar]

> Per has managed to change that file, and he didn't write it, so others
> do seem quite capable of figuring out what it does.

That of itself is not really relevant. I am sure there are people who can
manage to figure out almost anything, but to me the purpose of documentation
is precisely to *eliminate* the need to "figure out" what a given code unit
does. 

In the GNAT world, we always encourage new people reading the sources for the
first time to point out any place where they feel that more comments could
have made it easier to read. We almost always consider such comments prima
facie evidence of inadequate documentation, and we certainly don't think that
it is enough to point out that some experts very familiar with the system have
managed to figure things out.