Depending on where you saw the code, it is also used in non-literary sectors:
The code identifies a specific special edition of " Tess of the d'Urbervilles " by Thomas Hardy, released as part of the Prior on the Classics series. The "Story" Behind this Edition
: This edition is designed to help readers engage with the story through a Christian worldview. It includes an introduction and "Reading Closely" notes that prompt readers to think about the author’s original intent versus modern interpretations.