The Dewey decimal system is great, but there are systems of organization that are even better.

Twitter user Lauren Tarshis, for example, recently discovered that her 96-year-old mother-in-law, Stefanie Dreyfuss, recorded every single book she read on index cards using a secret code.

"I lost my mother in law last week. She was 96 and one of my best friends," Tarshis said. "A lifelong lover of books, she kept track of all she read on index cards and recorded her opinion in code. This is the key to her code and the cards we found among her belongings."

Here's a partial key to the code, in case you can't see from the photo:

RB: Readable Banality

RP: Readable Piffle

NFM: Not For Me

DNF: Did Not Finish

DNR: Did Not Read

RP+: One step up from RP

RPM: Readable piffle mystery

G: Good didn't hold my attention

VB: Very bad

NMS: Not my style

PB: Pretty boring

NBAL: Not bad at all

RR: Readable

WOT: Waste of Time

Obviously, this wonderful woman had genuine taste. I've never seen so many negative adjectives on a list.

My mother-in-law would have been beyond tickled by the interest in her code for rating books. For those who would like to know her better, here is her obituary. She was as beloved as she was fascinating. https://t.co/a7fgDEKvMT pic.twitter.com/DvYT6WyVOO — Lauren Tarshis (@laurenTarshis) May 27, 2018

Goodreads has a similar rating system, but it's nowhere near as advanced as this.

Let's all adopt the 96MIL (96-year-old Mother-In-Law) school of classification for books in the future.

IDW (it's deeply wise).