Processes and caches in postgresql

Hi, hackers.
There's a couple of questions about processes.

I found EXEC_BACKEND flag, while reading the code.
As I understood, it exists because we have to emulate fork() on WIN32.
And also it allows to debug the same behavior on Linux.
Is it right? Are there any other use cases?

Another question is about "--fork" argument (see code below).
I didn't find it in documentation, so I'm a bit confused.
I wonder if it exists only for internal purposes?

#ifdef EXEC_BACKEND
if (argc > 1 && strncmp(argv[1], "--fork", 6) == 0)
SubPostmasterMain(argc, argv); /* does not return */
#endif

And the last, but not least. Do we have any
presentations/articles/READMEs/whatever
about caches (src/backend/utils/cache/*) in postgresql?
I found nothing, besides comments in the code.

--
Anastasia Lubennikova
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company