Mopidy Discourse

Where is XDG_MUSIC_DIR set for server version of Mopidy

I see this shell variable used in many example configs. But I have not seen any explanation as to its purpose, or use. A general search of the term does not yield anything other than its use as a variable, not its setting.
So where should it be set for the Server Mopidy, and what to?
Is it the local path to the music (so the same as manually setting it in the config)?

Unfortunately, installing from the Pimoroni setup page and then following the Mopidy ‘step-by-step’ raspberry pi installation seems to leave the non-initiated with several holes in the installation process. This is one, another is the linking of /etc/asound.conf (which doesn’t exist at this point) etc.

My set up is,

INFO [MainThread] mopidy.main Starting Mopidy 3.1.1
DEBUG [MainThread] mopidy.ext Loading entry point: raspberry-gpio = mopidy_raspberry_gpio:Extension
DEBUG [MainThread] mopidy.ext Loaded extension: Mopidy-Raspberry-GPIO 0.0.2
DEBUG [MainThread] mopidy.ext Loading entry point: pidi = mopidy_pidi:Extension
DEBUG [MainThread] mopidy.ext Loaded extension: Mopidy-PiDi 1.0.3
DEBUG [MainThread] mopidy.ext Loading entry point: mpd = mopidy_mpd:Extension
DEBUG [MainThread] mopidy.ext Loaded extension: Mopidy-MPD 3.1.0
DEBUG [MainThread] mopidy.ext Loading entry point: local = mopidy_local:Extension
DEBUG [MainThread] mopidy.ext Loaded extension: Mopidy-Local 3.2.1
DEBUG [MainThread] mopidy.ext Loading entry point: iris = mopidy_iris:Extension
DEBUG [MainThread] mopidy.ext Loaded extension: Mopidy-Iris 3.57.6
DEBUG [MainThread] mopidy.ext Loading entry point: file = mopidy.file:Extension
DEBUG [MainThread] mopidy.ext Loaded extension: Mopidy-File 3.1.1
DEBUG [MainThread] mopidy.ext Loading entry point: http = mopidy.http:Extension
DEBUG [MainThread] mopidy.ext Loaded extension: Mopidy-HTTP 3.1.1
DEBUG [MainThread] mopidy.ext Loading entry point: m3u = mopidy.m3u:Extension
DEBUG [MainThread] mopidy.ext Loaded extension: Mopidy-M3U 3.1.1
DEBUG [MainThread] mopidy.ext Loading entry point: softwaremixer = mopidy.softwaremixer:Extension
DEBUG [MainThread] mopidy.ext Loaded extension: Mopidy-SoftwareMixer 3.1.1
DEBUG [MainThread] mopidy.ext Loading entry point: stream =
DEBUG [MainThread] mopidy.ext Loaded extension: Mopidy-Stream 3.1.1
DEBUG [MainThread] mopidy.ext Loading entry point: spotify = mopidy_spotify:Extension
DEBUG [MainThread] mopidy.ext Loaded extension: Mopidy-Spotify 4.1.0
DEBUG [MainThread] mopidy.ext Discovered extensions: raspberry-gpio, pidi, mpd, local, iris, file, http, m3u, softwaremixer, stream, spotify
DEBUG [MainThread] mopidy.config.keyring Fetching passwords from your keyring failed. Any passwords stored in the keyring will not be available.
INFO [MainThread] mopidy.config Loading config from builtin defaults
INFO [MainThread] mopidy.config Loading config from command line options
DEBUG [MainThread] mopidy.ext Validating extension: raspberry-gpio
DEBUG [MainThread] mopidy.ext Validating extension: pidi
DEBUG [MainThread] mopidy.ext Validating extension: mpd
DEBUG [MainThread] mopidy.ext Validating extension: local
DEBUG [MainThread] mopidy.ext Validating extension: iris
DEBUG [MainThread] mopidy.ext Validating extension: file
DEBUG [MainThread] mopidy.ext Validating extension: http
DEBUG [MainThread] mopidy.ext Validating extension: m3u
DEBUG [MainThread] mopidy.ext Validating extension: softwaremixer
DEBUG [MainThread] mopidy.ext Validating extension: stream
DEBUG [MainThread] mopidy.ext Validating extension: spotify
INFO [MainThread] mopidy.main Enabled extensions: pidi, local, iris, stream, softwaremixer, http, mpd, m3u
INFO [MainThread] mopidy.main Disabled extensions: spotify, raspberry-gpio, file
cache_dir = /var/cache/mopidy
config_dir = /etc/mopidy
data_dir = /var/lib/mopidy
max_tracklist_length = 10000
restore_state = false

verbosity = 0
format = %(levelname)-8s [%(threadName)s] %(name)s %(message)s
color = false
config_file =

mixer = software
mixer_volume = 40
output = alsasink device=hw:sndrpihifiberry
buffer_time =

scheme =
hostname =
port =
username =
password =

enabled = false ; Extension disabled by user config.

enabled = true
display = st7789
rotation = 90

enabled = true
hostname = ::
port = 6600
password =
max_connections = 20
connection_timeout = 60
zeroconf = Mopidy MPD server on $hostname
command_blacklist =
default_playlist_scheme = m3u

enabled = true
max_search_results = 999
media_dir = /home/pi/Music
scan_timeout = 2000
scan_flush_threshold = 100
scan_follow_symlinks = false
included_file_extensions =
excluded_file_extensions =
directories =
timeout = 10
use_artist_sortname = false
album_art_files =

enabled = true
country = NZ
locale = en_NZ
data_dir = $XDG_DATA_DIR/iris

enabled = false ; Extension disabled due to config errors.
media_dirs =
excluded_file_extensions =
show_dotfiles = false
follow_symlinks = false
metadata_timeout = 1000

enabled = true
hostname = ::
port = 6680
zeroconf = Mopidy HTTP server on $hostname
allowed_origins =
csrf_protection = true
default_app = mopidy

enabled = true
base_dir = /home/pi/Music/Playlists
default_encoding = latin-1
default_extension = .m3u8
playlists_dir = /home/pi/Music/Playlists

enabled = true

enabled = true
protocols =
metadata_blacklist =
timeout = 5000

enabled = false ; Extension disabled by user config.