`sig
type b_idx
val of_int_unsafe : int -> BatUTF8.Byte.b_idx
val to_int : BatUTF8.Byte.b_idx -> int
val next : BatUTF8.t -> BatUTF8.Byte.b_idx -> BatUTF8.Byte.b_idx
val prev : BatUTF8.t -> BatUTF8.Byte.b_idx -> BatUTF8.Byte.b_idx
val of_char_idx : BatUTF8.t -> BatUTF8.char_idx -> BatUTF8.Byte.b_idx
val at_end : BatUTF8.t -> BatUTF8.Byte.b_idx -> bool
val out_of_range : BatUTF8.t -> BatUTF8.Byte.b_idx -> bool
val first : BatUTF8.Byte.b_idx
val last : BatUTF8.t -> BatUTF8.Byte.b_idx
val move : BatUTF8.t -> BatUTF8.Byte.b_idx -> int -> BatUTF8.Byte.b_idx
end`