Conditional / Fallback source for form elements (dynaranges, combobxes, lists etc)

Problem / Use case: It is often required to have a conditional source in a form element.

• A dynarange/list/combobox might show only elements, when certain selections in the POV match some checks

• In large nested dynaranges only base elements of outer dynarange shall show the full hierarchy of the inner dynarange - consolidated elements in outer dynarange shall only show the root element of the inner dynarange (not expandable, since it's only one element), see table below

  
  

  All years	All Customers
  2020	All Customers
  	East
  	North

  
  

• A user wants to exchange outer and inner dynarange to look at data from a different perspective - since the dimension in a subset editor cannot be changed dynamically and also the subset in total might be completely different, a conditional source would allow for an alternative subset, so that they could be exchanged, when both subsets are defined in both dynaranges

How the above is currently achieved: When using a formula the designer obviously has all the flexibility to provide this capability. E.g. "=IF(PALO.ELEVEL(_con,_dim,DynaRange1)>0,_root_element,PALO.SUBSET(...))" would solve the second use case. The problem is, that this makes it harder to make any changes in the subset afterwards (since subset editor cannot be used to make changes in the subset) and also the formula input field is not really made for having large formulas in there.
So doing this currently requires a more or less deep knowledge of (subset) formulas and feels a bit clumsy.

Proposal: Introduce a new "fallback source". To accomplish that, it would be helpful to provide two new inputs in the definition of a form element. First input field would be a straight spreadsheet formula like the "visibility" of a form element, but it evaluates the usage of the actual source vs fallback source. As default it would contain the formula "=TRUE" - if the formula evaluates to TRUE, the actual source is used, if it evaluates to FALSE, the fallback source would be used. Second input would be the same as the actual source: either a formula, a subset (opens subset editor) or an ODBC query. As a MVP a formula only would also be sufficient.