The heart of TiddlyWiki can be seen as an extensible representation transformation engine for text and images. Given the text of a tiddler and its associated ContentType, the engine can produce a rendering of the tiddler in a new ContentType. Furthermore, it can efficiently selectively update the rendering to track any changes in the tiddler or its dependents.
The primary use of the engine is to convert raw `text/vnd.tiddlywiki` WikiText into a `text/html` or `text/plain` representation for display. The transclusion and templating features of WikiText allow the engine to also be used to generate TiddlyWiki HTML files from raw tiddlers.