One possibility is to set the property Sticky="true"
which prevents the tooltip from hiding when the
mouse moves away from the target element, so content in the tooltip
itself can be selected. The tooltip will close when the mouse moves out
Another possibility is to use the AutoCloseDelay property.
property specifies how many
milliseconds should elapse before the tooltip closes automatically if
the cursor is positioned over the element
(similar to the behavior of the default browser tooltip). Each movement
of the mouse resets the delay, and as a result, moving over a target
element without leaving its boundaries
would cause the tooltip to stay visible. The default setting of the AutoCloseDelay
property is 2000 milliseconds.
the Telerik team