1. How to add multi-line tooltip?
For button control, you can wrap the tooltip string in a TextBlock element, and then use either <LineBreak/> or 
 in the tooltip string.
If you set the tooltip using code, you can directly use “\n” in the tooltip text, :
2. How to add bolded texts to the tooltip?
Use <Run> element.
3. How to add images to the tooltip?
Use <InlineUIContainer> and <Image> elements.
