One of the symbols :upcase, :downcase, or :capitalize.

The symbol :upcase.

The value of *print-case* controls the case (upper, lower, or mixed) in which to print any uppercase characters in the names of symbols when vertical-bar syntax is not used.

*print-case* has an effect at all times when the value of *print-escape* is false. *print-case* also has an effect when the value of *print-escape* is true unless inside an escape context (i.e., unless between vertical-bars or after a slash).

 (defun test-print-case () 
   (dolist (*print-case* '(:upcase :downcase :capitalize)) 
     (format t "~&~S ~S~%" 'this-and-that '|And-something-elSE|))) 
→ TEST-PC 
;; Although the choice of which characters to escape is specified by 
;; *PRINT-CASE*, the choice of how to escape those characters 
;; (i.e., whether single escapes or multiple escapes are used) 
;; is implementation-dependent.  The examples here show two of the 
;; many valid ways in which escaping might appear. 
 (test-print-case) ;Implementation A 
⊳ THIS-AND-THAT |And-something-elSE| 
⊳ this-and-that a\n\d-\s\o\m\e\t\h\i\n\g-\e\lse 
⊳ This-And-That A\n\d-\s\o\m\e\t\h\i\n\g-\e\lse 
→ NIL 
 (test-print-case) ;Implementation B 
⊳ THIS-AND-THAT |And-something-elSE| 
⊳ this-and-that a|nd-something-el|se 
⊳ This-And-That A|nd-something-el|se 
→ NIL

write

read normally converts lowercase characters appearing in symbols to corresponding uppercase characters, so that internally print names normally contain only uppercase characters.

If *print-escape* is true, lowercase characters in the name of a symbol are always printed in lowercase, and are preceded by a single escape character or enclosed by multiple escape characters; uppercase characters in the name of a symbol are printed in upper case, in lower case, or in mixed case so as to capitalize words, according to the value of *print-case*. The convention for what constitutes a “word” is the same as for string-capitalize.