I first heard of this only recently. (At my age, a decade or so seems "recent.") It surprises me how well it works: If you put the adjectives in the wrong order, the phrase is likely to sound non-idiomatic.
Different sources give slightly different categories. Combining lists one can update Elixir's list of 9 categories to 11:
- Determiner/Quantity
- Opinion
- Size
- Physical Quality
- Age
- Shape
- Color
- Origin
- Material
- Type
- Purpose
- (Noun)
The rules are not absolute of course, and it's not always clear what category an adjective is in. But I am intrigued by how closely idiomatic English usually DOES adhere. (Have there been studies of adjective order in other languages?)
A fun little project is to construct phrases with long strings of adjectives and see how well the ordering rule applies. Any takers? I've attached two noun phrases with 11 adjectives each, one from each category. (The excessive number of adjectives will make them seem non-idiomatic regardless of order. Try saying them with some of the adjectives omitted. I didn't know what material to apply to girl, but went with 'silky-skinned.' I could have substituted a plastic sex robot for the girl but didn't want to seem perverted!)
An exquisite miniature sturdy antique triangular ebony-colored French ceramic flat heating iron
A serviceable tall gorgeous young buxom blond Swedish silky-skinned freelance working girl