.NET doesn't support arbitrary code points (`.` or `C`) outside the BMP

[Aloso]

• C could be polyfilled as (?:\P{Cs}|\p{IsLowSurrogates}\p{IsHighSurrogates})
• . could be polyfilled as (?:[^\n\p{Cs}]|\p{IsLowSurrogates}\p{IsHighSurrogates})

Polyfilling is only needed when it isn't repeated, or the repetition has a lower bound > 1 or an upper bound