What is Carte, and how is it related to css4j?

Carte was a publishing/reporting framework written in the Java™ programming language, and it used css4j for rendering. Css4j was initially smaller than Carte and was a subproject.

Carte was based on reporting extensions that were annotated into XHTML documents by using namespaces. But the new web APIs that emerged with html5 provided alternative (and potentially more attractive) ways to do the tasks that the framework was intended to perform. Also, when html5 appeared the prospects for the wide use of multiple namespaces in documents looked dim (and Carte depended on people being able/willing to compose such documents).

Most of Carte was discontinued and the css4j subproject became inactive, but after several years the development of css4j continued. Now css4j is much larger than Carte, and is hosted at https://github.com/css4j.

There is another 'css4j' project hosted at Sourceforge (css4j.sourceforge.net). Is this code related to it?

This project's CSS4J is unrelated to Sourceforge's 'css4j' project, a different project that decided to use the same name as this Carte's subproject. This project was the first to use the CSS4J name and publish source code under it, in February of 2006, while the 'other' CSS4J was created in October of that year. Although the author of the other project has provided this one with code snippets and suggestions, the software is otherwise unrelated.