CL, and its object system particularly, specifies a lot of extensibility and sometimes hilarious dynamicity with exacting detail. E.g. you can subclass a class that doesn't even exist yet (!)

  CL-USER> (defclass foo (bar) ())
  #<STANDARD-CLASS FOO>
  CL-USER> (find-class 'bar)
  #<FORWARD-REFERENCED-CLASS BAR>

That's just one detail, but CL is chock full of such niceties, owing to the fact that a lot of rivaling factions of super-smart programmers wanted to get all their favorite features into it.