Can anyone explain how CDbCriteria->scopes works?

I've just checked the man page of CDbCriteria, but there is not enough info about it. This property is available since v1.1.7 and I couldn't find any help for it. Is it for dynamically changing Model->scopes "on-the-fly"?

Scopes are an easy way to create simple filters by default. With a scope you can sort your results by specific columns automatically, limit the results, apply conditions, etc. In the links provided by @ldg there's a big example of how cool they are:

$posts=Post::model()->published()->recently()->findAll();

Somebody is retrieving all the recently published posts in one single line. They are easier to maintain than inline conditions (for example Post::model()->findAll('status=1')) and are encapsulated inside each model, which means big transparency and ease of use.

Plus, you can create your own parameter based scopes like this:

public function last($amount)
{
    $this->getDbCriteria()->mergeWith(array(
        'order' => 't.create_time DESC',
        'limit' => $amount,
    ));
    return $this;
}

Adding something like this into a Model will let you choose the amount of objects you want to retrieve from the database (sorted by its create time). By returning the object itself you allow method chaining.

Here's an example:

$last3posts=Post::model()->last(3)->findAll();

Gets the last 3 items. Of course you can expand the example to almost any property in the database. Cheers