COPYSIGN function copies the sign of a number on another one and pushes back the value.
Since 2.6.0, this function can be applied to a LIST of numerical values and a numerical value. Considering this function as
F, the result of
$a [ $b $c ] F is
[ $a $b F $a $c F ] and the result of
[ $a $b ] $c F is
[ $a $c F $b $c F ].
Since 2.7.1, this function can be applied to a GTS of numerical values. This is very similar to how this function works on LISTs, considering the values of the GTS. In that case the result is a GTS.