The syntax highlighter indicates that math.isnan should exist. However an attempt to use it results in an Attempt To Call A Nil Value error.
Image showing error and highlighting compared to both valid and invalid math.xx expressions: https://imgur.com/3xX9lNe
I lean toward fixing this by implementing math.isnan on principle of luau compatibility, but I don't have strong feelings about it either way. The number of likely users of math.isnan is incredibly small (
laughs
one?) and I'm perfectly comfortable with using v~=v. (It's more succinct!)