lispdoc - results for digit-char-p

(digit-char-p char &optional (radix 10))
Function: If char is a digit in the specified radix, returns the fixnum for which that digit stands, else returns NIL.
 Mentioned in:
CLtL2 - 13.2. Predicates on Characters
CLtL2 - 13.4. Character Conversions
HyperSpec - Function DIGIT-CHAR-P