First defined in: FKiSS4
The letsibling action sets the value of variable to the
lowest-numbered object attached to the same parent object as target
but with a higher object number than target.
If target is not attached to a parent object or if
target is the highest-numbered object attached to its parent
object, variable is set to -1.
variable
variable must be a variable name.
target
target may be an object number or a variable
representing an object number.
Example:
;@ letsibling(C, #5)
;@ letsibling(C, VarOrphan)