Visual Studio 2005 automatically enables IntelliSense - through reflection it detects all classes, properties and methods in the dll file(s).
For additional convenience each Telerik control is provided an XML file which contains the comments for its classes, properties and methods.
For example, when Telerik RadDock is dragged to the webform the RadDock.Net2.xml file is automatically added in the bin directory of the project.
In ASPX, when you start typing or when you insert a space, VisualStudio will show a dropdown with suggestions for autocomplete.
In code-behind, each time a particular class/property/method is being selected from the dropdown of the autocomplete functionality, a tooltip with the comment for this class/property/method is displayed:
