Solarsail -- not true. For one example, BNF is a meta-language (a language about language), and it is extremely useful in the real world. As the author of a c

Solarsail -- not true. For one example, BNF is a meta-language (a language about language), and it is extremely useful in the real world. As the author of a computer language expert system, I refer to its rules language as a meta-language (and rules as meta-code) because it manipulates language content symbolically. And, as it happens, it actually executes BNF in order to parse the languages it consumes, the BNF being delivered to it via that same rules language. Code content represented in my system's Internal Representation (IR) is not itself a meta-language; it's more of a "super-language", being synthesized across real languages. But that IR's architecture does comprise a kind of meta-language; because it is a structure that represents language content in an abstracted way, it is "about" the very concept of a computer language. As the author of such a system, I do meta every day, meta-meta often, and triple-meta occasionally.