RT - "Readers Grand Staff on a Timeline" - Identifies files of RT sheet music.
PG - "Prep, Grand Staff" - Identifies preparatory files for learning to play from the Grand Staff. Includes sheet music at the prep level.
-nn - Two digit number used to put the files in the desired order.
-v - Version
-vS - Standard Version
CO - "Color Octave Group" Notes are colored the colors of the octave groups in which they are located.
RC - "Repertoire Collections."
CS - Chord Symbols - The notation includes standard chord symbols.
Cds - Chords - The notation includes chords that are spelled out.
TITLES IN ALL CAPITALS - (PG-00) These are section titles. They have no content.
Titles with no content - (PG-50) These are simply spacers used to separate sections of the list.