Sorry for the late reply. As I previously stated, I can make hidden data elements by using action (or similar) containing data elements. But then, I need to use ancestor reference everywhere to access such elements. And after "Change Display Element to Data Element", ancestor reference is visible on data elements using it (which again should be hidden).
It's hard to say right now where do I find this feature useful, while I'm still having only an idea on my mind. Easiest way to think of it is to use OOP terms: each display element is a class having public and private members. Members can be atoms (variables/constants) or actions (methods) using atoms. Once there is satisfying class design, designer could use "Change Display Element to Data Element" to produce API. Furhther on, designer can use only API in his workflow (for libraries using this feature).
I have no idea how this could be implemented in Tersus right now, but I would like to have this feature to bring external libraries targeting multiple platforms (server or client side). In other words, instead of making plugins for Tersus which are tedious task to do (and probably only bringing subset of existing library functionalites), I would like to target existing libraries directly by exposing their API.
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