<p>I want to use the Date::ABBR_MONTHS constant in my rails application. I see the Ruby stdlib documentation at <a href="http://www.ruby-doc.org/stdlib/" rel="nofollow noreferrer">http://www.ruby-doc.org/stdlib/</a> which does not seem to have this constant. 
However, this constant is there at <a href="http://stdlib.rubyonrails.org/" rel="nofollow noreferrer">http://stdlib.rubyonrails.org/</a></p>

<p>What is the difference between these two libraries?</p>

<p>This constant is working on my unix deployment machine but not on my dev machine on windows. Can anybody explain whats going on?</p>

```
ABBR_MONTHS
```
is something you get given to you by ActiveSupport and it's just added into the Date class. The first library is for ruby, where the second one is for ruby on rails. The constant may not be working because of different versions of Rails.