When referencing a looping input map element in the output, it is necessary for all ancestor looping map elements in the input to have an associated output map element loop expression. Most often this occurs naturally if your output looping corresponds to the input looping. However, there are times when there is a gap in the correspondence, and this gap can be filled in using the NestedContext function by providing the instructions for handling the looping input elements that were not referenced by output elements.
To create a nested loop expression:
Create the outer loop expression - Drag the desired loop function to the loop expression tree, and then drag the desired input map element to the Input Map Element argument.
Create nested context - Drag the NestedContext function to the Contexts argument of the loop expression.
Specify the nested loop - Drag the desired inner loop function to the NestedContext expression, and then drag the desired inner input map element to the Input Map Element argument.