Document // as a prefix op

Author: lizmat

doc/Language/operators.pod6

@@ -39,7 +39,7 @@ level.
     Method call      | left          | .meth .\+ .? .* .() .[] .{} .<> .«» .:: .= .^ .: i
     Autoincrement    | non           | \+\+ --
     Exponentiation   | right         | **
-    Symbolic unary   | left          | ! \+ - ~ ? \| \|\| \+^ ~^ ?^ ^
+    Symbolic unary   | left          | ! \+ - ~ ? \| \|\| \+^ ~^ ?^ ^ //
     Dotty infix¹     | left          | .= .
     Multiplicative   | left          | * × / ÷ % %% \+& \+< \+> ~& ~< ~> ?& div mod gcd lcm
     Additive         | left          | \+ - − \+\| \+^ ~\| ~^ ?\| ?^
@@ -1161,6 +1161,17 @@ Coerces the argument to L<Bool|/type/Bool> by calling the C<Bool> method on it,
 and returns the negation of the result.
 Note that this collapses L<Junction|/type/Junction>s.
 
+=head2 prefix C«//»
+
+    multi sub prefix:<//>(Any --> Bool:D)
+
+X<Boolean context operator|Operators,Boolean context operator>.
+
+Available as of 6.e language version (early implementation exists in Rakudo
+compiler 2022.12+).
+
+Coerces the argument to L<Boolean|/type/Bool> by calling the C<defined> method on it.
+
 =head2 prefix C«+»
 
     multi sub prefix:<+>(Any --> Numeric:D)