The operator First valid value receives two or more inputs. It returns the first valid input. For example, if the first input does not match, the second is used.
Example
In the example, the Name attribute of the source is assigned to the Name attribute of the target. If the Name attribute is not specified in the source, the next attribute (Description/Definition)) is assigned to the Name attribute of the target, and so on.
If you combine the operator First valid value with the Find operator, the first matching result is used.