Since Throne totally stole my guess for the rule on the last game, I'm claiming partial moral victory and running my own game! Refer to Pedro's thread for rules, because I am lazy.
The sha-1 hash of the rule is a22f344e3ab8cb53d5b251943b69181ff99879a4.
The permitted format is strings (of positive integer length) of lower-case letters (standard English alphabet) and digits (0 through 9).
"raven" fits the rule, but "writing0desk" does not.