How do rails association methods work?

How do rails association methods work? Lets consider this example

class User < ActiveRecord::Base
   has_many :articles
end

class Article < ActiveRecord::Base
   belongs_to :user
end

Now I can do something like

@user = User.find(:first)
@user.articles

This fetches me articles belonging to that user. So far so good.

Now further I can go ahead and do a find on these articles with some conditions.

@user.articles.find(:all, :conditions => {:sector_id => 3})

Or simply declare and associations method like

class User < ActiveRecord::Base
   has_many :articles do
     def of_sector(sector_id)
       find(:all, :conditions => {:sector_id => sector_id})
     end
   end
end

And do

@user.articles.of_sector(3)

Now my question is, how does this find work on the array of ActiveRecord objects fetched using the association method? Because if we implement our own User instance method called articles and write our own implementation that gives us the exact same results as that of the association method, the find on the fetch array of ActiveRecord objects wont work.

My guess is that the association methods attach certain properties to the array of fetched objects that enables further querying using find and other ActiveRecord methods. What is the sequence of code execution in this this case? How could I validate this?