base.UTF16

imm .fromSurrogatePair(high: imm base.Nat, low: imm base.Nat): imm base.Str -> …,
imm .isSurrogate(codePoint: imm base.Nat): imm base.Bool -> …,
imm .fromCodePoint(codePoint: imm base.Nat): imm base.Str -> …,
imm .fromSurrogatePair(high: imm base.Nat, low: imm base.Nat): imm base.Str -> …,
imm .isSurrogate(codePoint: imm base.Nat): imm base.Bool -> …,
imm .fromCodePoint(codePoint: imm base.Nat): imm base.Str -> …,