I have just finished an extensive rewrite of book chapter 10. I’ve added much more material on USING and DROP. Besides an introduction to DSECTs, You’ll find a discussion of ordinary, labeled, dependent, and labeled dependent USING statements. There is an explanation of what the assembler is doing in pass one, and how the USING table is processed in pass two as you issue USING and DROP directives. I’ll probably come back and add some programming exercises, but for the moment, I’m done.
Many thanks to Ajith Thankappan for his helpful suggestions. You can find that chapter here and on the website.