The Package

The following function accepts a single character and returns a string containing a character reference entity for that character:

(defun escape-char (char)
  (case char
    (#\& "&")
    (#\> ">")
    (#\' "'")
    (#\" """)

You can also define two parameters: *element-escapes*, which contains the characters you need to escape in normal element data, and *attribute-escapes*, which contains the set of characters to be escaped in attribute values.

(defparameter *element-escapes* "<>&")
(defparameter *attribute-escapes* "<>&\"'")

Finally, you’ll need a variable, *escapes*, that will be bound to the set of characters that need to be escaped. It’s initially set to the value of *element-escapes*, but when generating attributes, it will, as you’ll see, be rebound to the value of *attribute-escapes*.