Where/How are the XDG_*_DIR user directory variables supposed to be set?

I'm referring to: https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html I have the following files in my

.config

directory:

~/.config/user-dirs.dirs

:

# ...
XDG_DOWNLOAD_DIR="$HOME/downloads"
# ... there are only comments in this file, except the line above ...

(I guess this file needs to be sourced somewhere? But where and how?)

~/.config/user-dirs.conf

:

enabled=False

(This file seems to be necesseary to prevent

-user-dirs-update

from overwriting

~/.config/user-dirs.dirs

.) However, **

$XDG_DOWNLOAD_DIR

is not set when I run a shell.** __Where/How are the XDG_*_DIR user directory variables supposed to be set?__ Am I supposed to source

~/.config/user-dirs.dirs

in one of the files sourced by my login shell (e.g. in

.bash_profile

)?