The bash man page is close to 40K words. It's not quite War and Peace, but it could hold its own in a rack of cheap novels. Given the size of bash's documentation, missing a useful feature is easy to do when looking through the man page. For that reason, as well as to look for new features, revisiting the man page occasionally can be a useful thing to do.
The sub-section of interest today is Parameter Expansion—that is, $var in its many forms. Don't be confused by the name though, it's really about parameter and variable expansion.