title: Understanding :source option of has_one/has_many through of Rails
body: <p>Please help me in understanding the <code>:source</code> option of <code>has_one/has_many :through</code> association. The Rails API explanation makes very little sense to me.</p>
  
  <blockquote>
    <p>"Specifies the source association name used by <code>has_many</code> <code>:through =&gt;
    :queries</code>. Only use it if the name cannot be inferred from the
    association. <code>has_many :subscribers, :through =&gt; :subscriptions</code> will
    look for either <code>:subscribers</code> or <code>:subscriber</code> on <code>Subscription</code>,
    unless a <code>:source</code> is given. "</p>
  </blockquote>