How to use [set-x]

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

Similar to [set-value], but does not evaluate expressions found in its source. Where [set-value] replaces a source expression with the value it points to, [set-x] assigns the expression itself as the new value of its destination nodes. It takes the same arguments as [set-value]; a main expression selecting the destination nodes, and at most one source child. Having more than one child throws an exception.

.foo1:.bar1
set-x:x:../*/.foo1
   .:x:../*/.foo1

After execution, the value of [.foo1] is the expression ../*/.foo1, and not the value .bar1.