The Javadoc for Eclipse QVT Operational 3.10.3 APIs (Mars release) may be found by following the Operational QVT 3.10.3 API Reference link.
There are three extension points.
org.eclipse.m2m.qvt.oml.javaBlackboxUnits.
org.eclipse.m2m.qvt.oml.runtime.qvtTransformation.
org.eclipse.m2m.qvt.oml.runtime.qvtTransformationContainer.