title: What is the ActiveModel method attribute "_was" used for?
body: <p>When using autocomplete in the console, I often see "<code>_was</code>" postpended to my attributes. But I can't find any documentation or best practices for usage. What does it do and how should it be used?</p>
  
  <p>Example: <code>user.fname</code> has the method <code>user.fname_was</code></p>
  
  <p>Using source_location, I've tracked it down to: active_model/attribute_methods.rb", line 296 but there isn't anything specific.</p>