Yii core messages refer to static text strings in the core Yii framework code which are meant to be displayed to end-users (e.g. core exception messages, default validation error messages). Customization of these core messages is needed in two circumstances:
By default, the expression Yii::app()->user returns a CWebUser application component which represents the information that are closely related with the current user. Some information can be persistent throughout the current user session. For example, CWebUser already comes with a name property that stores the username of the current user.
A dropdown list can be used to select a value, based on which we can filter the data to be displayed. For example, the extension page has a dropdown list to filter the displayed extensions according to the selected category.
A simple and effective way to keep track what your users are doing within your application is to log their activities related to database modifications. You can log whenever a record was inserted, changed or deleted, and also when and by which user this was done. For a CActiveRecord Model you could use a behavior for this purpose. This way you will be able to add log functionality to ActiveRecords very easily.
Validators extending from CValidator all have a property named message. You can set this property in the corresponding validation rule to customize the error message. For example, the following validation rule uses an error message that is different from the default one: