This demo explains how the tooltips can show data from the datasource without actually performing an AJAX request or calling a WebService each time one is shown which can ultimately increase the server performance.
The main concept is to add targets for the RadToolTipManager so that the tooltipified elements can be configured precisely, but instead of configuring a LOD scenario the necessary information can be sent to the client in the Value property for each target. This information can be obtained on the server, for example from the same datasource. Then, a simple JavaScript function attached to the OnClientShow event can take the data and put it in the tooltip. In the demo a simple HTML structure is used as a template to create a more appealing presentation and reduce the JavaScript that is needed.
In this demo data from the grid's datasource is concatenated for each tooltip, but the general case is to just get a string, e.g. a localized hint related to a button on the page.
This logic is suitable for data that will not change much over time and not all of it is necessary in the main view of the page. The approach is similar to the Data Caching mechanism, but avoids the tooltips' requests to the server at all (except the ones for the images, of course, but they are simple GET requests and not postbacks).
NOTE: The data must serialize in a JSON string, so the developer must make sure to escape it properly, otherwise the page may break. For example, \n, \r (or vbLf and vbCr in VB), apostrophes, quotes should be escaped in order work well with JavaScript. The HttpUtility.UrlEncodeUnicode method can be used (although marked as obsolete in .NET 4.5) because it can be decrypted easily on the client with decodeURIComponent while UrlEncode replaces spaces with plus signs.