If you specify "browser" for this property, the user control will be varied by browser type and major version number. You can also use this property to extend the values that output cache varies the user control response.
The following code example demonstrates how the PartialCachingAttribute(Int32, String, String, String) constructor can be applied to a user control. In the example, the constructor is used to indicate that the user control can be cached and to specify that the cache entry is dependent on the browser type and major version number.
// Set the PartialCachingAttribute.Duration property to // 20 seconds and the PartialCachingAttribute.VaryByCustom // property to browser.
[PartialCaching(20, null, null, "browser")]
publicpartialclass ctlSelect : UserControl