lispdoc - results for with-output-to-sequence

 (var &key as-list (element-type ''octet) transformer) &body body)
Function: Creates an IN-MEMORY output stream, binds VAR to this stream and then executes the code in BODY. The stream stores data of type ELEMENT-TYPE (a subtype of OCTET) which is (optionally) transformed by the function TRANSFORMER prior to storage. The stream is automatically closed on exit from WITH-OUTPUT-TO-SEQUENCE, no matter whether the exit is normal or abnormal. The return value of this macro is a vector (or a list if AS-LIST is true) containing the octets that were sent to the stream within BODY.
(with-output-to-string (var &optional string &key (element-type ''character))
 &body forms-decls)
(defun process-coords (input)
  (with-output-to-string (s)
    (format-number s input)))
Mentioned in:
CLtL2 - 21.2. Creating New Streams
CLtL2 - 21.3. Operations on Streams
CLtL2 - 9.1. Declaration Syntax
On Lisp - Symbols and Strings
PCL - other kinds of io
PCL - strings in binary files
Successful Lisp - chapter19