[basic.fundamental] Exhaustively list what values can be represented by floating-point types

Author: eisenwave

source/basic.tex

@@ -5549,6 +5549,20 @@
 The standard and extended floating-point types
 are collectively termed \defnx{floating-point types}{type!floating-point}.
 \begin{note}
+A floating-point type can represent at least a subset of rational numbers.
+Depending on the implementation-defined value representation for the type,
+it can additionally represent a
+\begin{itemize}
+\item negative zero,
+\item positive infinity,
+\item negative infinity,
+\item set of quiet ``Not a Number'' values, and
+\item set of signaling ``Not a Number'' values.
+\end{itemize}
+A floating-point type which adheres to \IsoFloatUndated{}
+is capable of representing all of the above\iref{numeric.limits.members}.
+\end{note}
+\begin{note}
 Any additional implementation-specific types representing floating-point values
 that are not defined by the implementation to be extended floating-point types
 are not considered to be floating-point types, and