Most changes from review comments implemented. Remove use of "#elif" for

backward PP compatability. Add BOOST_category_item_AVAILABLE as a
defined, or not, symbol for use with "#ifdef" or "#ifndef". Add
documentation of macros used for detection and version information. Also
replace direct use of BVN(0,0,0) and BVN(0,0,1) with more meaningful
macros that are globally defined, and hence consistent.

include/boost/predef/language/objc.h

@@ -23,11 +23,15 @@ http://www.boost.org/LICENSE_1_0.txt)
     ]
  */
 
-#define BOOST_LANG_OBJC BOOST_VERSION_NUMBER(0,0,0)
+#define BOOST_LANG_OBJC BOOST_VERSION_NUMBER_NOT_AVAILABLE
 
 #if defined(__OBJC__)
 #   undef BOOST_LANG_OBJC
-#   define BOOST_LANG_OBJC BOOST_VERSION_NUMBER(0,0,1)
+#   define BOOST_LANG_OBJC BOOST_VERSION_NUMBER_AVAILABLE
+#endif
+
+#if BOOST_LANG_OBJC
+#   define BOOST_LANG_OBJC_AVAILABLE
 #endif
 
 #define BOOST_LANG_OBJC_NAME "Objective-C"

include/boost/predef/language/stdc.h

@@ -26,7 +26,7 @@ If available, the year of the standard is detected as YYYY.MM.1 from the Epoc da
     ]
  */
 
-#define BOOST_LANG_STDC BOOST_VERSION_NUMBER(0,0,0)
+#define BOOST_LANG_STDC BOOST_VERSION_NUMBER_NOT_AVAILABLE
 
 #if defined(__STDC__)
 #   undef BOOST_LANG_STDC
@@ -34,13 +34,17 @@ If available, the year of the standard is detected as YYYY.MM.1 from the Epoc da
 #       if (__STDC_VERSION__ > 100)
 #           define BOOST_LANG_STDC BOOST_PREDEF_MAKE_YYYYMM(__STDC_VERSION__)
 #       else
-#           define BOOST_LANG_STDC BOOST_VERSION_NUMBER(0,0,1)
+#           define BOOST_LANG_STDC BOOST_VERSION_NUMBER_AVAILABLE
 #       endif
 #   else
-#       define BOOST_LANG_STDC BOOST_VERSION_NUMBER(0,0,1)
+#       define BOOST_LANG_STDC BOOST_VERSION_NUMBER_AVAILABLE
 #   endif
 #endif
 
+#if BOOST_LANG_STDC
+#   define BOOST_LANG_STDC_AVAILABLE
+#endif
+
 #define BOOST_LANG_STDC_NAME "Standard C"
 
 #include <boost/predef/detail/test.h>

include/boost/predef/language/stdcpp.h

@@ -35,17 +35,21 @@ Specifically the defined versions are:
     ]
  */
 
-#define BOOST_LANG_STDCPP BOOST_VERSION_NUMBER(0,0,0)
+#define BOOST_LANG_STDCPP BOOST_VERSION_NUMBER_NOT_AVAILABLE
 
 #if defined(__cplusplus)
 #   undef BOOST_LANG_STDCPP
 #   if (__cplusplus > 100)
 #       define BOOST_LANG_STDCPP BOOST_PREDEF_MAKE_YYYYMM(__cplusplus)
 #   else
-#       define BOOST_LANG_STDCPP BOOST_VERSION_NUMBER(0,0,1)
+#       define BOOST_LANG_STDCPP BOOST_VERSION_NUMBER_AVAILABLE
 #   endif
 #endif
 
+#if BOOST_LANG_STDCPP
+#   define BOOST_LANG_STDCPP_AVAILABLE
+#endif
+
 #define BOOST_LANG_STDCPP_NAME "Standard C++"
 
 #include <boost/predef/detail/test.h>
@@ -67,17 +71,21 @@ If available, the year of the standard is detected as YYYY.MM.1 from the Epoc da
     ]
  */
 
-#define BOOST_LANG_STDCPPCLI BOOST_VERSION_NUMBER(0,0,0)
+#define BOOST_LANG_STDCPPCLI BOOST_VERSION_NUMBER_NOT_AVAILABLE
 
 #if defined(__cplusplus_cli)
 #   undef BOOST_LANG_STDCPPCLI
 #   if (__cplusplus_cli > 100)
 #       define BOOST_LANG_STDCPPCLI BOOST_PREDEF_MAKE_YYYYMM(__cplusplus_cli)
 #   else
-#       define BOOST_LANG_STDCPPCLI BOOST_VERSION_NUMBER(0,0,1)
+#       define BOOST_LANG_STDCPPCLI BOOST_VERSION_NUMBER_AVAILABLE
 #   endif
 #endif
 
+#if BOOST_LANG_STDCPPCLI
+#   define BOOST_LANG_STDCPPCLI_AVAILABLE
+#endif
+
 #define BOOST_LANG_STDCPPCLI_NAME "Standard C++/CLI"
 
 #include <boost/predef/detail/test.h>
@@ -96,11 +104,15 @@ BOOST_PREDEF_DECLARE_TEST(BOOST_LANG_STDCPPCLI,BOOST_LANG_STDCPPCLI_NAME)
     ]
  */
 
-#define BOOST_LANG_STDECPP BOOST_VERSION_NUMBER(0,0,0)
+#define BOOST_LANG_STDECPP BOOST_VERSION_NUMBER_NOT_AVAILABLE
 
 #if defined(__embedded_cplusplus)
 #   undef BOOST_LANG_STDECPP
-#   define BOOST_LANG_STDECPP BOOST_VERSION_NUMBER(0,0,1)
+#   define BOOST_LANG_STDECPP BOOST_VERSION_NUMBER_AVAILABLE
+#endif
+
+#if BOOST_LANG_STDECPP
+#   define BOOST_LANG_STDECPP_AVAILABLE
 #endif
 
 #define BOOST_LANG_STDECPP_NAME "Standard Embedded C++"