PAX has been around since 1992 so probably predates any "rules"

Is also a Swedish word, though slang, the imperative form of paxa which basically means the same as "dibs!" If I know my english colloquialisms correctly.

The exception that proves the rule :)

It reminds some system - they didn’t allow “other” category for sorting features, but someone came with “999” :)

Clue to their DB setup?