There is only 4 commands, represented by next characters
H: print "Hello, world!"
Q: print the program's source code (a Quine)
9: print the lyrics to "99 Bottles of Beer"
+: add one to the accumulator (the value of the accumulator cannot be accessed)
Any other character is ignored.

Ok. Let's write some program:
  HQ9

Result:
  Hello world!
  HQ9

HQ9+ is very simple, but allows you to do some things that are very difficult
in other languages. For example, here is a program that creates three copies of
itself on the screen:
  QQQ

This produces:
  QQQ
  QQQ
  QQQ