* lib/mkmf.rb (MakeMakefile#dir_config): Improve documentation.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45533 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,7 @@
+Tue Apr  8 22:55:32 2014  Akinori MUSHA  <knu@iDaemons.org>
+
+	* lib/mkmf.rb (MakeMakefile#dir_config): Improve documentation.
+
 Tue Apr  8 22:31:44 2014  Koichi Sasada  <ko1@atdot.net>
 
 	* gc.c: rename `RGENGC_THREEGEN' to `RGENGC_AGE2_PROMOTION'.

lib/mkmf.rb

@@ -1677,13 +1677,28 @@ SRC
     $extconf_h = header
   end
 
-  # Sets a +target+ name that the user can then use to configure various
-  # "with" options with on the command line by using that name.  For example,
-  # if the target is set to "foo", then the user could use the
-  # <code>--with-foo-dir</code> command line option.
+  # call-seq:
+  #   dir_config(target)
+  #   dir_config(target, prefix)
+  #   dir_config(target, idefault, ldefault)
   #
-  # You may pass along additional "include" or "lib" defaults via the
-  # +idefault+ and +ldefault+ parameters, respectively.
+  # Sets a +target+ name that the user can then use to configure
+  # various "with" options with on the command line by using that
+  # name.  For example, if the target is set to "foo", then the user
+  # could use the <code>--with-foo-dir=prefix</code>,
+  # <code>--with-foo-include=dir</code> and
+  # <code>--with-foo-lib=dir</code> command line options to tell where
+  # to search for header/library files.
+  #
+  # You may pass along additional parameters to specify default
+  # values.  If one is given it is taken as default +prefix+, and if
+  # two are given they are taken as "include" and "lib" defaults in
+  # that order.
+  #
+  # In any case, the return value will be an array of determined
+  # "include" and "lib" directories, either of which can be nil if no
+  # corresponding command line option is given when no default value
+  # is specified.
   #
   # Note that dir_config only adds to the list of places to search for
   # libraries and include files.  It does not link the libraries into your