Chapters 1 through 5 are devoted to extending the set of nodes, actions, and elements in the database. Understanding how to create new nodes and actions requires some background information that was not needed in Open Inventor Mentor, 2nd Edition - Volume I. Important concepts discussed in this chapter include the method list, state and elements, the stack index, caching, runtime typing, and using extender macros. Most of the topics introduced in this chapter are discussed in detail in later chapters. Figure 1.1, “ Summary of SoEXTENDER Classes ” shows a summary of key SoEXTENDER classes.