net.lisp: Add docstring for `string-subipnet'.

diff --git a/net.lisp b/net.lisp
index 1750da0..7480b3c 100644 (file)
--- a/net.lisp
+++ b/net.lisp
@@ -376,6 +376,7 @@
 
 (export 'string-subipnet)
 (defun string-subipnet (ipn str &key (start 0) (end nil))
+  "Parse an IP subnet from a parent net IPN and a suffix string STR."
   (setf str (stringify str))
   (let* ((addr-class (extract-class-name (ipnet-net ipn)))
         (width (ipaddr-width addr-class))