The viewing of documents is not responsibility of these programs. Usually viewing and editing is made by structured editors, that are integrated with the program using the API tools. The queries will return only whole documents. Search for parts of documents is not possible. The documents can be retrieved using this information.
Most languages are data or event driven.
Actions or character strings in the input select a conversion rule and a process. Because SGML does not involve a specified grammar but can be used to describe texts for different kinds of grammars, SGML parsers are actually meta parsers. They input a grammar and generate a parser according to this grammar. Mostly a set of functions or procedure libraries that are used to allow a program to interface with other programs. The representations of programs contain following features in addition of a short description.