Note that the property is valid after 2013 Q3 and above.
As of Q3 2013 release, we introduced a feature that is related to the filtering of the RadAutoCompleteBox - Client Filtering. The functionality could be easily managed by the EnableClientFiltering property, which accepts two values : true or false.
Unlike the default behavior of the control, a callback is not fired upon each character typed in the input area. In contrast to that, if the Client Filtering is enabled, the RadAutoCompleteBox is initially supplied with the underlying DataSource. When you type characters in the input of the control, you only manage the visibility of the already loaded data.
The Client Filtering could be very useful, if the RadAutoCompleteBox is populated with a third part WebService or ODataSource. As the filtering could not be custom implemented in such databinding scenarios, the usage of the Client Filtering is quite appropriate.
We recommend using the Client-Filtering feature in a scenario when small amount of data is used for the RadAutoCompleteBox population. Considering the fact that the entire data is initially retrieved, iterating trough a large items collection could reflect as a slow-responsive page.