Meaning of file flags

[Rocky Hotas <rockyhotas%firemail.cc@localhost>]

Hello!
In a recent and very interesting thread here, file flags are mentioned.
Manpage chflags(1) shows their list. But what about their meaning?
I've found this old message:

 <https://mail-index.netbsd.org/tech-security/1999/02/01/0000.html>

where short descriptions of flags are shown. However, I still can't
understand the meaning of `nodump' and `arch'.
Is there another reference/document/message about them?
Bye,

Rocky