  Grammars are used to describe sentences structure, thanks to some sets of
rules, which depends on the grammar type. A classification of grammars has been
made by Noam Chomsky, which led to four well-known types. Yet, there are other
types of grammars, which do not exactly fit in Chomsky's classification, such
as the two-level grammars. As their name suggests it, the main idea behind
these grammars is that they are composed of two grammars. Van Wijngaarden
grammars, particularly, are such grammars. They are interesting by their power
(expressiveness), which can be the same, under some hypotheses, as the most
powerful grammars of Chomsky's classification, i.e. Type 0 grammars. Another
point of interest is their relative conciseness and readability. Van
Wijngaarden grammars can describe static and dynamic semantic of a language.
So, by using them as a generative engine, it is possible to generate a possibly
infinite set of words, while assuring us that they all have the same semantic.
Moreover, they can describe K-ary codes, by describing the semantic of each
components of a code.
