Fixtype of validation tables.
This is a product type introduced by fty::defprod.
Scopes are treated in a stack-like manner [C:6.2.1]. Thus, we define a validation table as containing a list (i.e. stack) of scopes. The stack grows from right to left: the leftmost scope is the top, and the rightmost scope is the bottom; in other words, in the nesting of scopes in the stack, the leftmost scope is the innermost, and the rightmost scope is the outermost (i.e. the file scope [C:6.2.1/4].)
We wrap the list of scopes into a fty::defprod for abstraction and extensibility.