- add more doc to Model
- CompareValidator::clientValidateAttribute(): search for "CHtml::activeId"
- FileValidator, UniqueValidator, ExistValidator, DateValidator: TBD
- Can consider merging UniqueValidator and ExistValidator and using a NOT property.
- design of component life cycles: init() and afterConstruct()
	* construct object
	* preinit
	* attachBehaviors
	* initialize properties
	* init
	* ...
	* destruct
- get/setFlash() should be moved to session component
- support optional parameter in URL patterns