It is a sound engineering practice to avoid using keywords as names even when the language’s parser will let you get away with it. For consistency, some developers (myself included) will avoid words like `class` and `module` even when embedded in a longer name, such as `user_class`.

I don’t use `klass`, but that’s because I’m a Java Bigco cubicle-dweller fraudulently passing himself off as a Rubyist and Javascripter. I prefer `clazz` in keeping with Sun examples.

class is a keyword.

I use `cls` in my ruby code, as I do in other langs; I think `klass` is unsightly.

klass is used in meta programming as a way to control scope.

The author of the code must like German. He used "Matz" as a parameter, a German name, and klass = class in German.