Theoretically, you can make this happen, however, some tweaks are required:
1. The Window is by default scrollable. You must disable this behavior by using
2. The validation message is not a tooltip (although it reuses some of the tooltip's styles). It is part of the page's so called "normal flow". You need to make it an absolutely positioned element via CSS.
Note that the white-space:nowrap style should not be needed, as the validation messages have it applied by default. I am not sure why this does not work in your case, maybe something else overrides the style.
3. Some top
styles might also be needed to position the validation message according to your preferences.
All the best,
the Telerik team
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