BTW, you can write: arr.each(function(el){...}); in Prototype as well, and you can attach custom method to JS array accepting functor "on the fly", it will loo

BTW, you can write: arr.each(function(el){...}); in Prototype as well, and you can attach custom method to JS array accepting functor "on the fly", it will look unfamiliar to beginners, but it will be still JS. There is a definition for what author tries to explain: Embedded Domain Specific Language Here is the def: http://c2.com/cgi/wiki?EmbeddedDomainSpecificLanguage http://c2.com/cgi/wiki?EmbeddedDomainSpecificLanguage Many powerful languages provide cool constructs for creating embedded domain specific languages that look very different from the base language, just take a look at Ruby or LISP or C++. You can also take a look at metaprogramming (writing programs that create other programs). http://en.wikipedia.org/wiki/Metaprogramming http://en.wikipedia.org/wiki/Metaprogramming