It is useful to view a wiki page as a composition of content fragments where we have content generators like templates, extensions, and parser functions injecting content fragments onto the page. Wikifunctions is yet another fragment generator entering the picture. Whenever the output of a fragment changes (ex: a template is edited, wikifunction code is updated), there is no reason to regenerate the content of the entire page from scratch. It is more efficient to use the existing output and selectively update the fragment in-place. This is harder to implement for templates today in the general case since output of templates is not guaranteed to be a well-structured fragment. But, there is a lot of benefit to such a solution, specifically for wikifunctions.

T363421: Prototype selective HTML updates in Parsoid is the first step in this process.