ActiveSupport is one of the gems that makes up Rails and provides a lot of useful helper methods. When working in Ruby, you can load the entire ActiveSupport library with the following command:
ActiveSupport is a large library and it is better to only require portions of it if possible. For example, if you would like to take advantage of the blank? method in Rails, use this line:
ActiveSupport time helpers are particularly useful and can be required with this line:
Once ActiveSupport#time is included, useful methods like ago() and months() are accessible in the Rails application.
>> 5.months.ago => 2013-03-13 20:05:03 -0400
The RailsGuides have more information about loading ActiveSupport Core Extensions.