It's pretty universal to use syntax that's outside the domain of the language being described to describe a language in it's specification, otherwise your head

It's pretty universal to use syntax that's outside the domain of the language being described to describe a language in it's specification, otherwise your head would explode trying to distinguish the example from the rule. The C++ standard uses tables for the equivalent purpose, not C++ declarations, like at §23.2.1 in C++11. Does this mean that C++ should move from header files to an RDBMS?