[docs,io,format] Improve control string docs.

* documentation/library-reference/source/io/format.rst: Link to
  DRM docs about control strings. Also, convert to using lowercase
  characters in the control strings as that's more common (%s instead
  of %S).

documentation/library-reference/source/io/format.rst

@@ -10,11 +10,11 @@ Introduction
 
 This chapter describes the Format module. The Format module is exported
 from the IO library. This module extends the functionality of the format
-strings described in Dylan's condition system and provides two new
-functions for processing the extended format strings. The Format module
-is a small module, but it uses the printing modules and some of the
-Streams module. :doc:`print` and :doc:`streams` give full details of
-the Print and Streams libraries.
+strings described in :drm:`Dylan's condition system <Condition_Messages>`
+and provides two new functions for processing the extended format strings.
+The Format module is a small module, but it uses the printing modules and
+some of the Streams module. :doc:`print` and :doc:`streams` give full
+details of the Print and Streams libraries.
 
 The ``format`` module exports all the identifiers described in this
 chapter.
@@ -23,8 +23,9 @@ Control strings
 ===============
 
 The Format module's format strings, or control strings, offer the same
-directives as Dylan's format strings offer, but Format provides a few
-more directives, and permits a single argument to all format directives.
+directives as :drm:`Dylan's format strings <Condition_Messages>` offer,
+but Format provides a few more directives, and permits a single argument
+to all format directives.
 
 The argument is an integer that must appear contiguously between the
 dispatch character, ``%``, and the format directive. The argument
@@ -37,35 +38,35 @@ specification. The following are examples of valid format directives:
 
 ::
 
-    %S
     %s
-    %15D
+    %S
+    %15d
     %-10=
 
 The directives are:
 
-- ``%S`` Prints the next format argument as a message by calling the
+- ``%s`` Prints the next format argument as a message by calling the
   function :gf:`print-message` on the format argument and the stream.
-  This directive is the same as Dylan's ``%S`` format-string directive
-  except for two features: (i) this module's ``%S`` directive outputs
-  character objects, and (ii) you can extend the ``%S`` functionality by
+  This directive is the same as Dylan's ``%s`` format-string directive
+  except for two features: (i) this module's ``%s`` directive outputs
+  character objects, and (ii) you can extend the ``%s`` functionality by
   adding methods to :gf:`print-message`.
 - ``%=`` Prints the next format argument by calling the :gf:`print`
   function from the Print module on the format argument and the stream.
   You can extend the ``%=`` functionality by adding methods to the
   :gf:`print-object` function from the Print module.
-- ``%C`` Print the next format argument, which must be a character,
-  according to Dylan's ``%S`` format-string directive. This module's
-  ``%C`` directive is the same as this module's ``%S`` directive.
-- ``%D`` Prints a decimal representation of the next format argument,
+- ``%c`` Print the next format argument, which must be a character,
+  according to Dylan's ``%s`` format-string directive. This module's
+  ``%c`` directive is the same as this module's ``%s`` directive.
+- ``%d`` Prints a decimal representation of the next format argument,
   which must be an integer.
-- ``%B`` Prints a binary representation of the next format argument,
+- ``%b`` Prints a binary representation of the next format argument,
   which must be an integer.
-- ``%O`` Prints an octal representation of the next format argument,
+- ``%o`` Prints an octal representation of the next format argument,
   which must be an integer.
-- ``%X`` Prints a hexadecimal representation of the next format
+- ``%x`` Prints a hexadecimal representation of the next format
   argument, which must be an integer.
-- ``%M`` Invokes the next format argument, which must be a function, on
+- ``%m`` Invokes the next format argument, which must be a function, on
   the stream passed to :gf:`format`.
 - ``%%`` Outputs a single ``%`` character.
 
@@ -165,8 +166,8 @@ Format module.
 
      See the individual methods for the details of how this function
      prints various objects. This function exists to define the behavior
-     of the ``%S`` format directive and to allow users the ability to
-     extend the ``%S`` directive. Users should have little need to call
+     of the ``%s`` format directive and to allow users the ability to
+     extend the ``%s`` directive. Users should have little need to call
      this function directly.
 
 .. method:: print-message
@@ -181,7 +182,7 @@ Format module.
    :description:
 
      Prints ``condition`` as an error message, as described for the
-     Dylan ``%S`` format directive. You should not specialize the
+     Dylan ``%s`` format directive. You should not specialize the
      :gf:`print-message` protocol for subclasses of :drm:`<condition>`, but
      instead extend the :gf:`print-message` protocol to new condition
      objects by specializing methods on :gf:`report-condition`.