You can see how to popupate the TargetControls collection in this help article: http://www.telerik.com/help/aspnet-ajax/tooltipmanager-targetcontrols.html
. You can do this either in the markup, or in the code-behind (e.g. in the PageLoad when the page is not posted back).
If you need static strings and you do not need dynamic updates there are two ways you can do this:
1) add the desired string to the Value property of the target control item, then in the OnClientShow event set this value as the text, e.g.:
2) set the strings you need in your controls' tooltip or alt property (i.e. as default browser tooltips) and turn on the Autotooltipify feature of the RadToolTipManager which will automatically replace them with RadToolTips. You can see it in action in this online demo
Note that you must not have an OnAjaxUpdate event handler attached for both approaches to work so simply, as the main purpose of the ToolTipManager is to load content on demand.
All the best,
the Telerik team
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