Implementations of the {@link org.apache.tapestry.IEngine} interface, including the standard implementation: {@link org.apache.tapestry.engine.SimpleEngine}. Also located here are default implementations of all the basic support objects, including {@link org.apache.tapestry.engine.RequestCycle} (which implements {@link org.apache.tapestry.IRequestCycle}). @author Howard Lewis Ship hlship@apache.org