How to use [set-value]

The reference page of set-value has its arguments, constraints and declaration.

Changes the value of all nodes referenced as its main expression to whatever its single source happens to be. Notice, when you invoke a slot that tries to change the value, name, or the node itself of some expression, and you supply a source expression to your invocation - Then the result of the source expression cannot return more than one result. The destination expression however can modify multiple nodes simultaneously.

.foo
.foo
set-value:x:../*/.foo
   .:SUCCESS