Questions about staging

[Montgomery-Smith, Stephen]

I am looking at this part of https://wiki.freebsd.org/ports/StageDir

Replace commands like ${CHMOD} ... and ${INSTALL_PROGRAM} -m mode -o
user -g group with corresponding pkg-plist entries: @mode mode, @owner
user, @group group.
/!\ These operators work until being overridden, or until the end of
pkg-plist, so do not forget to reset them with @mode, @owner, @group
keywords afterwards.

I have to admit that I don't understand what this is driving at.  Can
someone explain it to me?