Bret calls Tangle a library for coding Reactive Documents and I like this idea very much. He has a good explanation of the philosophy behind it in his own words:
I don’ t think I can add much yet to what he says already. What I do find interesting is one of his lasts question in the above article.
Its a very interesting question. We might also combine this idea and question with other interesting projects online that bring in dynamic authoring functionality. For an example the Mercury Editor is an important step in this direction with its dynamic snippets.
Whats cool about all of this is that all of the interesting stuff, explorations and implementations are Open Source. The benefits of Open Source in this world is really starting to pay off and I think the world of book production is going to blossom in this area while closed source projects get left behind.