NB: More recent documentation for Dyalog APL is available at https://docs.dyalog.com/20.0/.

Variant {R}←{X}(f ⎕OPT B)Y

⎕OPT is synonymous with the Variant Operator ⍠ and can be used in both Classic and Unicode Editions - unlike ⍠ which is valid in Unicode Editions only, and ⎕U2360 which is valid in Classic Editions only.

See Variant.