Add a new feature that allows designating a field as a required sub-property.

[yancao77]

Is it possible to add a new feature that enables the designation of a field "F" as a required sub-property within the element "E" (0-N)? This would imply that if there is an instance of "E", the "F" field must be filled. However, if there is no instance, it can remain empty.

[graybeal]

I believe that to get what you want, a restatement may make it more precise. As I understand the desire, the F field must be filled if and only if E, the element within which F appears, has some meaningful values. (You can only tell if "there is an instance of E" if some field within E has content. Elements themselves don't have filled-out values, only their fields do.) So then the question becomes, for each element, how to know if it has meaningful content.

So I can think of 4 use cases that might be useful to satisfy:

1. If some other field G of element E is filled, then F must also be filled. (This rule would also hold for any 'iteration of E', where E is MULTIPLE=Yes—then field G of iteration i of element E being filled means field F of iteration i of element E must be filled.
2. If any non-F field of element E is filled, field F must also be filled. (Also holds for iterations of E.)
3. If some field external to element E is filled, field F inside element E must also be filled (for all iterations of E).
4. Instead of 'the field is filled' in 1 thru 3 above, the constraint could be 'the field passes some test', like value > 30, value="Test", or number of values > 1.
5. Boolean combinations and negations of the above. (Ick.)

I laid it out this way because I suspect this is a variant or analog of skip logic, also discussed in

• Question Skipping & Form Navigation metadatacenter-attic/cedar-features#16
• caDSR-style question skipping #933
• Investigate question skipping vs wizards #535

In the skip logic case, the question is whether a field should be displayed. In this case, the question is whether a field should be required. Both require display-time evaluation of some value or values in an arbitrary computation; this case also requires validation-time execution.