Improve Doxygen docs for nested namespaces

	* doc/doxygen/doxygroups.cc (std::tr2, std::__gnu_cxx): Improve docs.
	(std::experimental): Add docs.
	* doc/doxygen/user.cfg.in (PREDEFINED): Expand macros for __cxx11
	namespace to nothing when generating docs.
	* include/bits/regex_constants.h (std::regex_constants): Improve docs.
	* include/std/chrono (std::chrono): Likewise.
	* include/std/functional (std::placeholders): Likewise.
	* include/std/thread (std::this_thread): Likewise.

From-SVN: r270805

libstdc++-v3/ChangeLog

 2019-05-02  Jonathan Wakely  <jwakely@redhat.com>
 
+	* doc/doxygen/doxygroups.cc (std::tr2, std::__gnu_cxx): Improve docs.
+	(std::experimental): Add docs.
+	* doc/doxygen/user.cfg.in (PREDEFINED): Expand macros for __cxx11
+	namespace to nothing when generating docs.
+	* include/bits/regex_constants.h (std::regex_constants): Improve docs.
+	* include/std/chrono (std::chrono): Likewise.
+	* include/std/functional (std::placeholders): Likewise.
+	* include/std/thread (std::this_thread): Likewise.
+
 	* include/parallel/settings.h: Fix Doxygen markup.
 
 	* include/ext/pb_ds/detail/bin_search_tree_/*_imps.hpp: Do not define

libstdc++-v3/doc/doxygen/doxygroups.cc

@@ -29,13 +29,15 @@
  *  @brief Implementation details not part of the namespace std::tr1 interface.
 */
 /** @namespace std::tr2
- *  @brief ISO C++ TR2 entities toplevel namespace is std::tr2.
+ *  @brief Namespace for non-standard "TR2" extensions.
+ *  @ingroup extensions
 */
 /** @namespace std::tr2::__detail
  *  @brief Implementation details not part of the namespace std::tr2 interface.
 */
 /** @namespace __gnu_cxx
  *  @brief GNU extensions for public use.
+ *  @ingroup extensions
 */
 /** @namespace __gnu_cxx::__detail
  *  @brief Implementation details not part of the namespace __gnu_cxx 
@@ -45,6 +47,9 @@
  *  @brief GNU implemenation details, not for public use or
  *  export. Used only when anonymous namespaces cannot be substituted.
 */
+/** @namespace std::experimental
+ *  @brief Namespace for features defined in ISO Technical Specifications.
+ */
 // // // // // // // // // // // // // // // // // // // // // // // //
 
 /**

libstdc++-v3/doc/doxygen/user.cfg.in

@@ -2265,10 +2265,12 @@ PREDEFINED             = __cplusplus=201402L \
                          "_GLIBCXX_BEGIN_NAMESPACE_VERSION= " \
                          "_GLIBCXX_BEGIN_NAMESPACE_ALGO= " \
                          "_GLIBCXX_BEGIN_NAMESPACE_CONTAINER= " \
+                         "_GLIBCXX_BEGIN_NAMESPACE_CXX11= " \
                          "_GLIBCXX_BEGIN_NAMESPACE_LDBL= " \
                          "_GLIBCXX_END_NAMESPACE_VERSION= " \
                          "_GLIBCXX_END_NAMESPACE_ALGO= " \
                          "_GLIBCXX_END_NAMESPACE_CONTAINER= " \
+                         "_GLIBCXX_END_NAMESPACE_CXX11= " \
                          "_GLIBCXX_END_NAMESPACE_LDBL= " \
                          "_GLIBCXX_TEMPLATE_ARGS=...  " \
                          _GLIBCXX_DEPRECATED \
@@ -2290,6 +2292,7 @@ PREDEFINED             = __cplusplus=201402L \
                          PB_DS_DATA_TRUE_INDICATOR \
                          PB_DS_STATIC_ASSERT=// \
                          "_GLIBCXX_BEGIN_NAMESPACE_ALGO= " \
+                         "_GLIBCXX_END_NAMESPACE_ALGO= " \
                          __glibcxx_function_requires=// \
                          __glibcxx_class_requires=// \
                          __glibcxx_class_requires2=// \

libstdc++-v3/include/bits/regex_constants.h

@@ -43,7 +43,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 /**
  * @namespace std::regex_constants
- * @brief ISO C++-0x entities sub namespace for regex.
+ * @brief ISO C++ 2011 namespace for options and flags used with std::regex
  */
 namespace regex_constants
 {

libstdc++-v3/include/std/chrono

@@ -54,7 +54,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    */
 
   /** @namespace std::chrono
-   *  @brief ISO C++ 2011 entities sub-namespace for time and date.
+   *  @brief ISO C++ 2011 namespace for date and time utilities
    */
   namespace chrono
   {

libstdc++-v3/include/std/functional

@@ -199,7 +199,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   template<int _Num> struct _Placeholder { };
 
   /** @namespace std::placeholders
-   *  @brief ISO C++11 entities sub-namespace for functional.
+   *  @brief ISO C++ 2011 namespace for std::bind placeholders.
    *  @ingroup binders
    */
   namespace placeholders

libstdc++-v3/include/std/thread

@@ -328,8 +328,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   /** @namespace std::this_thread
-   *  @brief ISO C++ 2011 entities sub-namespace for thread.
-   *  30.3.2 Namespace this_thread.
+   *  @brief ISO C++ 2011 namespace for interacting with the current thread
+   *
+   *  C++11 30.3.2 [thread.thread.this] Namespace this_thread.
    */
   namespace this_thread
   {