-plus or minus sign begins with ``INFINITY'' or ``NAN'', ignoring
-case, it is interpreted as an infinity or a quiet NaN, respectively.
+plus or minus sign begins with
+.Dq INFINITY
+or
+.Dq NAN ,
+ignoring case, it is interpreted as an infinity or a quiet \*(Na,
+respectively.
+The syntax
+.Dq Xo Pf NAN( Ar "s" ) Xc ,
+where
+.Ar s
+is an alphanumeric string, produces the same value as the call
+.Fo nan
+.Qq Ar s Ns
+.Fc
+(respectively,
+.Fo nanf
+.Qq Ar s Ns
+.Fc
+and
+.Fo nanl
+.Qq Ar s Ns
+.Fc . )