assert.3: Update as per C23

Signed-off-by: Faraz Vahedi <kfv@kfv.io>

Author: kfv

share/man/man3/assert.3

@@ -25,7 +25,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd April 20, 2021
+.Dd May 17, 2026
 .Dt ASSERT 3
 .Os
 .Sh NAME
@@ -76,13 +76,17 @@ is defined determines the behavior of assert from that point forward
 until the end of the unit or another include of
 .In assert.h .
 .Pp
+In C23 and later, the
+.Fn assert
+uses ellipsis as the parameter.
+.Pp
 The
 .Fn assert
 macro should only be used for ensuring the developer's expectations
 hold true.
 It is not appropriate for regular run-time error detection.
 .Pp
-The
+In pre-C23 compilation modes, the
 .Fn static_assert
 macro expands to
 .Fn _Static_assert ,
@@ -96,6 +100,13 @@ The initial form of the
 containing a string literal message was introduced in C11 standard, and
 the other form with no string literal is to be implemented by C2x and
 some compilers may lack its adoption at present.
+.Pp
+In C23 and later,
+.Fn static_assert
+is a language keyword, and
+.Fn _Static_assert
+is provided as an obsolescent alternative spelling that should not be
+used for new code and development..
 .Sh EXAMPLES
 The assertion:
 .Dl "assert(1 == 0);"
@@ -123,12 +134,18 @@ If none is provided, it only points at the constraint.
 The
 .Fn assert
 macro conforms to
-.St -isoC-99 .
+.St -isoC-99
+and
+.St -isoC-2023 ,
+depending on the compilation mode.
 .Pp
 The
 .Fn static_assert
-macro conforms to
-.St -isoC-2011 .
+conforms to
+.St -isoC-2011 ,
+wherein defined as a macro, and
+.St -isoC-2023 ,
+as a language keyword, depending on the compilation mode.
 .Sh HISTORY
 An
 .Nm