What is the purpose of an indexTags setting of Group\:Work

[haggis999]

Hi Simon,
Several years ago, you kindly helped me to refine a MinimServer configuration that met my needs. The current version of that configuration is shown below. I am now trying to generate a document for my own education that explains exactly how this works, but I am struggling to understand the Group\:Work setting at the end of my indexTags, a setting whose origin has now been forgotten.

What exactly does that setting achieve? I would normally have experimented with deleting it to see the effects, but my NAS broke down earlier today!

==========================================
aliasTags=Work:Group
.autoUpdate=true
contentDir=/volume1/music/My Music
displayName=MinimServer[BonzoNAS]
http.port=9790
indexTags=CLASSICALGENRE=Classical:Classical library, NONCLASSICALGENRE=Non-classical:Non-classical library, Sub-Genre, Composer, Artist, DiscType, Group\:Work
itemTags=Genre
.logFile=minimserver.log
.logLevel=info
mergeFolderAlbums=true
ohnet.debug=Default
ohnet.port=9791
showExtras=false
startupScan=true
stream.converter=ffmpeg
stream.transcode=*:wav
tagCustom=Composer.displayRole={artist}
tagFormat=Artist.displayFormat={$composer}, Group.displayFormat={$group^$disctype^ [^]}, Title.displayFormat={$title^$disctype^ [^]}
tagOptions=Album.sortTags={Album, Artist}
tagUpdate=/volume1/music/My Music/MyTagUpdate.txt
.updateReminder=1
writeTagChanges=/volume1/music/My Music/MyMinimServerTags.txt

MyTagUpdate.txt
@GENRE=Classical
+CLASSICALGENRE=Classical
@GENRE=Non-classical
+NONCLASSICALGENRE=Non-classical