This JavaScript flavour of DuraLex is largely inspired by the original
DuraLex written in Python by promethe42:
* similar result of a semantic tree (slight modifications in the dialect)
* similar visitors manipulating the semantic tree to enhance it

However it differs in the syntactic recognition: the original DuraLex in
Python is a set of Python functions recognising parts of text, and this
version is constructed on a grammar then compiled to JavaScript functions
thanks to PEG.js.

Note that the PEG.js grammar dialect is near the Parsimonious grammar
dialect in Python; possibly they could be transformed through a
bijective mapping if some constraints are enforced on the writing (e.g.
there is no regex in PEG.js vs ( "aa" / "bb" / … ) are quite slow in
Parsimonious and should be rewritten to ~"aa|bb").

This version of DuraLex uses the grammar of metslesliens: essentially
the so-called references in DuraLex (the subjects of the sentences, i.e.
the location of the change) are parsed by metslesliens, and DuraLex
grammar parses the global sentences. Then DuraLex refines the resulting
raw tree thanks to the visitors, so that the final refined result is
useful for real applications like creating a diff.

Diffs are created in a form called “exact diffs”, which means “diffs
corresponding exactly to the modification described by the modifying
text” (and not diffs created by an independent algorithm). These diffs
are character-based, so that merges are vastly easier (and with better
results) than line-based diffs. With this level of precision, it is
probably safe to state that non-merging exact diffs are real political
alternatives (« en discussion commune »).