The XL programming language cannot be defined independently from a set of predefined core Java classes. These classes are, among others, the core classes of the Java programming language in the package java.lang, e.g., Object, Class, and String, classes in the package de.grogra.reflect, and a set of classes in subpackages of de.grogra.xl. Classes are referred to by their canonical name, or by their simple name if their package is obvious from context.