Is it possible to write field validation code in Display format section of Ruleset template without showing it on RMA screen. Is there any way to do it?
The short answer is no. If the standard providers don't give enough validation (only integers in an integer fields, only dates in the date provider), then you will need to build a custom provider to do the validation.
The other option is if you want only a value from a defined list, then set up a list provider to contain the list and force a choice from the dropdown that will be created.
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