Help: Cross reference CXX_STANDARD and CXX_EXTENSIONS (#16162)

Help/prop_tgt/CXX_EXTENSIONS.rst

@@ -6,7 +6,8 @@ Boolean specifying whether compiler specific extensions are requested.
 This property specifies whether compiler specific extensions should be
 used.  For some compilers, this results in adding a flag such
 as ``-std=gnu++11`` instead of ``-std=c++11`` to the compile line.  This
-property is ``ON`` by default.
+property is ``ON`` by default. The basic C++ standard level is
+controlled by the :prop_tgt:`CXX_STANDARD` target property.
 
 See the :manual:`cmake-compile-features(7)` manual for information on
 compile features and a list of supported compilers.

Help/prop_tgt/CXX_STANDARD.rst

@@ -22,6 +22,8 @@ with a compiler which does not support ``-std=gnu++11`` or an equivalent
 flag will not result in an error or warning, but will instead add the
 ``-std=gnu++98`` flag if supported.  This "decay" behavior may be controlled
 with the :prop_tgt:`CXX_STANDARD_REQUIRED` target property.
+Additionally, the :prop_tgt:`CXX_EXTENSIONS` target property may be used to
+control whether compiler-specific extensions are enabled on a per-target basis.
 
 See the :manual:`cmake-compile-features(7)` manual for information on
 compile features and a list of supported compilers.

Help/prop_tgt/C_EXTENSIONS.rst

@@ -6,7 +6,8 @@ Boolean specifying whether compiler specific extensions are requested.
 This property specifies whether compiler specific extensions should be
 used.  For some compilers, this results in adding a flag such
 as ``-std=gnu11`` instead of ``-std=c11`` to the compile line.  This
-property is ``ON`` by default.
+property is ``ON`` by default. The basic C standard level is
+controlled by the :prop_tgt:`C_STANDARD` target property.
 
 See the :manual:`cmake-compile-features(7)` manual for information on
 compile features and a list of supported compilers.

Help/prop_tgt/C_STANDARD.rst

@@ -22,6 +22,8 @@ with a compiler which does not support ``-std=gnu11`` or an equivalent
 flag will not result in an error or warning, but will instead add the
 ``-std=gnu99`` or ``-std=gnu90`` flag if supported.  This "decay" behavior may
 be controlled with the :prop_tgt:`C_STANDARD_REQUIRED` target property.
+Additionally, the :prop_tgt:`C_EXTENSIONS` target property may be used to
+control whether compiler-specific extensions are enabled on a per-target basis.
 
 See the :manual:`cmake-compile-features(7)` manual for information on
 compile features and a list of supported compilers.