GMC Envoy Owner's Manual page 223

The player will be able to read and play a maximum of
50 folders, 50 playlists, 10 sessions, and 255 files.
Long file, folder, or playlist names or a combination of a
large number of files and folders or playlists may
cause the player to be unable to play up to the
maximum number of files, folders, playlists, or sessions.
If you wish to play large numbers of files, folders,
playlists or sessions minimize the length of the file,
folder or playlist name. You can also play an MP3 CD
that was recorded using no file folders. The system can
support up to 11 folders in depth, though, keep the
depth of the folders to a minimum in order to keep
down the complexity and confusion in trying to locate
a particular folder during playback. If a CD contains
more than the maximum of 50 folders, 50 playlists,
10 sessions, and 255 files the player will let you access
and navigate up to the maximum, but all items over
the maximum will be ignored.
Root Directory
The root directory will be treated as a folder. If the root
directory has compressed audio files, the directory
will be displayed as F1 ROOT. All files contained directly
under the root directory will be accessed prior to any
root directory folders. However, playlists (Px) will always
be accessed before root folders or files.
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Empty Directory or Folder
If a root directory or a folder exists somewhere in the
file structure that contains only folders/subfolders and no
compressed files directly beneath them, the player will
advance to the next folder in the file structure that
contains compressed audio files and the empty folder
will not be displayed or numbered.
No Folder
When the CD contains only compressed files, the files will
be located under the root folder. The next and previous
folder functions will have no function on a CD that was
recorded without folders or playlists. When displaying the
name of the folder the radio will display ROOT.
When the CD contains only playlists and compressed
audio files, but no folders, all files will be located under
the root folder. The folder down and the folder up
buttons will search playlists (Px) first and then go to the
root folder. When the radio displays the name of the
folder the radio will display ROOT.