It's a pity that Nagel did not take a slight stroll on the wild side and call his book simply "Subversion Control". The actual title is logically correct but sounds redundant. Like the misbegotten phrase "The Los Angeles Angels". But if he'd chosen the shortened version, it would sound like a Homeland Security brochure.

Subversion is offered as a big improvement over the dominant CVS. The book describes a deliberately similar command line approach. With the same syntax for Subversion commands that map to corresponding CVS commands.

Perhaps the single biggest improvement is the better handling of directories. You can now version these just as you would files. This may be very apropos if you have a complex project. Where directories can encode high level structural decisions that may be as important as any subset of actual code.