I highly recommend editing both of these in "Edit source" mode, they are extremely buggy or fully non-functional in the Visual Editor. (You can still edit articles that contain them with the Visual Editor, as long as you don't touch these two elements)
Content to hover
Hello, this is a very very
very long tooltip content text for the purpose of showcasing how tooltips handle very very very very very long texts such as this one. Thank you and have a nice day!
Tooltip newline test.
Double newline for empty line. Most markdown seems to work fine as seen on the first line!
Simple tooltip for copypaste Hello world (Copy me in "Edit source" mode!)
Always visible text to hover This only appears while hovering (EDIT TEST GREEN)