- "Call FUNCTION with the pathname for each entry in DIRECTORY as follows: if
-FILES is true (the default), FUNCTION is called for each file in the
-directory; if DIRECTORIES is true (the default), FUNCTION is called for each
-subdirectory. If ERRORP is true (the default) signal an error if DIRECTORY
-does not exist, cannot be read, etc.
+ "Map over entries in DIRECTORY. Keyword arguments specify which entries to
+map over, and how:
+
+ :FILES
+ If true, call FUNCTION with the pathname of each file in DIRECTORY.
+ Defaults to T.
+
+ :DIRECTORIES
+ If true, call FUNCTION with a pathname for each subdirectory of DIRECTORY.
+ If :AS-FILES, the pathname used is a pathname designating the subdirectory
+ as a file in DIRECTORY. Otherwise the pathname used is a directory
+ pathname. Defaults to T.
+
+ :ERRORP
+ If true, signal an error if DIRECTORY does not exist, cannot be read, etc.
+ Defaults to T.