lower-case-p, upper-case-p

(lower-case-p character) (upper-case-p character)

lower-case-p returns t if character is a lowercase letter, upper-case-p if it is an uppercase letter, and nil otherwise. A character counts as lowercase exactly when upcasing it changes it (and uppercase when downcasing changes it), so both follow the platform's Unicode case tables. Available on all backends except --no-gc.