1.4. What it is not🔗

Triptych is not a general parser generator. Its grammar tier has concatenation, finite alternation, optional items, three built-in token classes, inclusive ASCII ranges, and separated repetition. A delimiter-bounded final payload may compute its exact width from earlier captures with syntax such as bit{upperTriangleSize Order}, but recursive productions and general capture-dependent boundaries remain outside the generated surface. The scanner architecture can compose a parsed header with a generated tail grammar for those broader cases, while automatic artifacts for that composition remain in progress. General Base64 is not yet expressible because the grammar has no arbitrary finite character class or unseparated repetition of a nonterminal.

That narrowness is what buys full automation. Within the class, everything is generated and proven with zero obligations; at the boundary, escape hatches let the accepted language be any decidable predicate and the parsed value be any type, at the cost of a small manual contract. A later chapter maps the gradient in detail.