Md5 documentation (newbie)

I’m going through the online documentation for Ruby 1.8.4 and looking
at Digest/MD5 classes and methods. There is one class method for the MD5
class, which is md5.

I have Ruby 1.8.2 but this md5 function doesn’t seem to be supported.
The way to hash something on my computer is to use hexdigest method of
the MD5 class yet I can’t see it in the 1.8.4 online documentation.

Could this be a difference in Ruby versions or am i missing something?
I’m not really a wiz bang programmer but i find reading the PHP
documentation a litte easier (its got examples and stuff).