If I typed in ` (a backtick), it creates invalid yaml.
If I typed in "Woohoo", it creates "Woohoo" in yaml, but it should be more like "Woohoo".
If I typed in "Quoth" said the Raven., it creates invalid yaml.
Ok lol, this one circumvents your solution in the video: If I typed in "Key: Value" it creates invalid yaml because it ends up as ""Key: Value"". :D
If I typed in ?, it creates invalid yaml.
Related to above: if I typed in "?" it's fine. Then I change another value in the same file, the "?" becomes ? and creates invalid yaml.
Anything that contains more than A-Z, 0-9, - and _ should get wrapped with "", and any " inside the text should be escaped out. That's the simplest approach I think.