An obvious possibility of broadening grammatical formalism without context is to allow non-terminals to argue arguments whose values are conveyed in the rules. This naturally allows for the expression of linguistic characteristics such as agreement and reference, as well as programming language analogs such as correct use and definition of identifiers. This allows us to express easily. B the fact that the subject and the verb must correspond by number in the English sentences. In computer science, you can see U-grade grammars, attribute grammars, indexed grammars and van Wijngaarden`s two-tiered grammars. Similar extensions exist in linguistics. A grammar without context provides a simple and mathematically accurate mechanism for describing the methods used to construct sentences in a natural language composed of smaller blocks, the « block structure » being naturally captured by sentences. Its simplicity makes formalism accessible to rigorous mathematical studies. Important characteristics of natural syntactic language such as concordance and reference are not part of grammar without context, but the basic recursive structure of sentences, how clauses are interwoven into other clauses, and how lists of adjectives and adverbs of verbs and verbs are swallowed are accurately described. Algorithms are known to be eliminated from a particular grammar without changing their generated language, unlike well-formed clips and hooks in the previous section, there is no contextual-free grammar to generate all sequences of two different types of parentheses, each balanced separately, without ignoring the other, where the two types do not need to be nested in each other. , for example: select S as your starting symbol.
This alternative grammar generates x-y-z with an analysis tree similar to that of the upper left, i.e. implicitly the association (x-y) -z, which does not follow the default order of operations. More complex, clearer and contextless grammars can be created, producing parse trees that follow all the rules of priority and association desired. A second canonical example are two different types of assigned nested staples that are described by productions: contextless grammars are formed in linguistics, where they are used to describe the structure of sentences and words in a natural language, and they were indeed invented by linguist Noam Chomsky for this purpose. In computer science, on the other hand, they have been increasingly used with the use of recursively defined concepts. In an early application, grammars are used to describe the structure of programming languages. In a recent application, they are used in a significant part of the Markup Language (XML) EXtensible, called document type definition.  Languages generated by non-context grammars are called language without context (CFL).