By default, when the TargetControls collection of the RadToolTip manager is empty, the manager iterates through all elements on the page, finds the ones that have a Title/Tooltip attribute set and tooltipifies them. There are situations however, when you want to use this functionality for a particular element, rather than the whole page.
In order to tooltipify just a part of the page, all you need to do is add a RadToolTip manager to the page and set its ToolTipZoneID to the ClientID of the element, that wraps that part. This functionality is particularly useful when you want to tooltipify a control, that renders complex HTML - for example RadGrid or RadScheduler. Just adding the ID of such a control to the TargetControls collection of the RadToolTip manager will result in the manager tooltipifying only the HTML element with the same ClientID as the control (in most cases - the outer most HTML element), instead of tooltipifying its child controls with Title/Tooltip attributes.
Note, that when you set the ToolTipZoneID property of the RadToolTip manager and the TargetControls collection of the manager is not empty, the manager will tooltipify all elements, that are inside the element with ID specified as ToolTipZoneID and have a Title/ToolTip attribute set.