This is a bit of a catch 22. The class was initially in spi, however we then decided that we actually don't want to expose it (hence the move). Sure there is still a getter in AbstractDocumentBuilder, but moving of the class itself into impl was supposed to indicate that it is not supposed to be used by integrators.

I actually think the crux is really that we have an abstract class in an spi package. I am wondering whether we should have a real DocumentBuilder interface (in spi) and then move the abstract class into the impl package.