The article is actually about a
revisit.
Lots of folks could spend similar time getting familiar with the core classes, be it just in irb/ripl (the REPL) using Object#methods, Class#instance_methods &c., using the command-line ri tool (e.g. $ ri Array) or one of the web-based doco sites: rubydoc.info, ruby-doc.org or apidock.com.
