Systems for writing documents roughly fall into two categories. In the first category, we find so called markup systems. Such systems are specified in terms of the syntax of the input language. Typical systems in this category are TeX, Texinfo, etc. In the second category, we find systems that allow the user to produce documents interactively. These systems are specified in terms of the gestures that the user can emit in different situations. Typical systems in this category are Word and LibreOffice.
Systems in both these categories specify only input and output. Both types of system generate output in some form that the user can view using standard tools, such as PDF or HTML. In addition, interactive tools typically use an external format that makes it possible to save and restore a document across editing sessions.
Unfortunately, users have very specific taste, both when it comes to input syntax and available gestures. For that reason, we think it is worth thinking about a system for manipulating documents in a different way.
The main observation is that systems in both categories are closed in that they do not allow the user to provide different ways of manipulating the document in the internal form that the system uses internally. The reason is probably that these systems are written in static languages, and so can not be easily customized to process a document in a way different from what the initial author of the system intended.
The purpose of this project is to create a library that defines a set of classes and generic functions that allow some client code to create and manipulate a document. Contrary to the types of systems cited above, the specification of this system is thus in terms of what kind of objects it manipulates, and what functions exist to manipulate them.
A library like this can then be used both by an application that reads some markup syntax and produces the document in the form of a graph of class instances, and by an interactive application that allows the user to create the document by issuing gestures. In fact, it will be possible to create several different application with different markups and with a different set of possible gestures.