See https://docs.basex.org/wiki/XQuery_Extensions - [ ] [Ternary If](https://docs.basex.org/wiki/XQuery_Extensions#Ternary_If) `$ok ?? 1 !! 0` - [x] [Elvis Operator](https://docs.basex.org/wiki/XQuery_Extensions#Elvis_Operator) - [x] [If Without Else](https://docs.basex.org/wiki/XQuery_Extensions#If_Without_Else)
See https://docs.basex.org/wiki/XQuery_Extensions
$ok ?? 1 !! 0