def modify(name, old_value, new_value)
      @attributes[name] = new_value
      if @modifications && (old_value != new_value)
        original = @modifications[name].first if @modifications[name]
        @modifications[name] = [ (original || old_value), new_value ]
      end
    end
def modify(name, old_value, new_value)
      @attributes[name] = new_value
      if @modifications && (old_value != new_value)
        original = @modifications[name].first if @modifications[name]
        @modifications[name] = [ (original || old_value), new_value ]
      end
    end
Audit the change of a field's value.

 Example:

 <tt>person.modify("name", "Jack", "John")</tt>