ANSI Common Lisp 22 Printer 22.1 The Lisp Printer 22.1.3 Default Print-Object Methods
220.127.116.11 Printing SymbolsWhen printer escaping is disabled, only the characters of the symbol's name are output (but the case in which to print characters in the name is controlled by *print-case*; see Section 18.104.22.168.2 Effect of Readtable Case on the Lisp Printer).
The remainder of this section applies only when printer escaping is enabled.
When printing a symbol, the printer inserts enough single escape and/or multiple escape characters (backslashes and/or vertical-bars) so that if read were called with the same *readtable* and with *read-base* bound to the current output base, it would return the same symbol (if it is not apparently uninterned) or an uninterned symbol with the same print name (otherwise).
For example, if the value of *print-base* were 16 when printing the symbol face, it would have to be printed as \FACE or \Face or |FACE|, because the token face would be read as a hexadecimal number (decimal value 64206) if the value of *read-base* were 16.