Below is the API for the OCaml standard library. It's directly copied over from the OCaml Manual, formatted to the Reason syntax and styled accordingly. The API docs are work-in-progress; we'll be polishing these gradually!
If you're targeting JavaScript, the API docs for BuckleScript includes all of below, plus JS-specific APIs.
module Array3: sig .. endArray3 structure provides operations
   similar to those of Bigarray.Genarray, but specialized to the case
   of three-dimensional arrays.type ('a, 'b, 'c) t 
'a, representation kind 'b, and memory layout 'c.val create : ('a, 'b) Bigarray.kind ->       'c Bigarray.layout -> int -> int -> int -> ('a, 'b, 'c) tArray3.create kind layout dim1 dim2 dim3 returns a new bigarray of
     three dimension, whose size is dim1 in the first dimension,
     dim2 in the second dimension, and dim3 in the third.
     kind and layout determine the array element kind and
     the array layout as described for Bigarray.Genarray.create.val dim1 : ('a, 'b, 'c) t -> intval dim2 : ('a, 'b, 'c) t -> intval dim3 : ('a, 'b, 'c) t -> intval kind : ('a, 'b, 'c) t -> ('a, 'b) Bigarray.kindval layout : ('a, 'b, 'c) t -> 'c Bigarray.layoutval get : ('a, 'b, 'c) t -> int -> int -> int -> 'aArray3.get a x y z, also written a.{x,y,z},
     returns the element of a at coordinates (x, y, z).
     x, y and z must be within the bounds of a,
     as described for Bigarray.Genarray.get;
     otherwise, Invalid_argument is raised.val set : ('a, 'b, 'c) t -> int -> int -> int -> 'a -> unitArray3.set a x y v, or alternatively a.{x,y,z} <- v,
     stores the value v at coordinates (x, y, z) in a.
     x, y and z must be within the bounds of a,
     as described for Bigarray.Genarray.set;
     otherwise, Invalid_argument is raised.val sub_left : ('a, 'b, Bigarray.c_layout) t ->       int -> int -> ('a, 'b, Bigarray.c_layout) tBigarray.Genarray.sub_left for more details.  Array3.sub_left
     applies only to arrays with C layout.val sub_right : ('a, 'b, Bigarray.fortran_layout) t ->       int -> int -> ('a, 'b, Bigarray.fortran_layout) tBigarray.Genarray.sub_right for more details.  Array3.sub_right
     applies only to arrays with Fortran layout.val slice_left_1 : ('a, 'b, Bigarray.c_layout) t ->       int -> int -> ('a, 'b, Bigarray.c_layout) Bigarray.Array1.tBigarray.Genarray.slice_left for more details.
     Array3.slice_left_1 applies only to arrays with C layout.val slice_right_1 : ('a, 'b, Bigarray.fortran_layout) t ->       int -> int -> ('a, 'b, Bigarray.fortran_layout) Bigarray.Array1.tBigarray.Genarray.slice_right for more details.
     Array3.slice_right_1 applies only to arrays with Fortran
     layout.val slice_left_2 : ('a, 'b, Bigarray.c_layout) t ->       int -> ('a, 'b, Bigarray.c_layout) Bigarray.Array2.tBigarray.Genarray.slice_left for more details.
     Array3.slice_left_2 applies only to arrays with C layout.val slice_right_2 : ('a, 'b, Bigarray.fortran_layout) t ->       int -> ('a, 'b, Bigarray.fortran_layout) Bigarray.Array2.tBigarray.Genarray.slice_right for more details.
     Array3.slice_right_2 applies only to arrays with Fortran
     layout.val blit : ('a, 'b, 'c) t -> ('a, 'b, 'c) t -> unitBigarray.Genarray.blit for more details.val fill : ('a, 'b, 'c) t -> 'a -> unitBigarray.Genarray.fill for more details.val of_array : ('a, 'b) Bigarray.kind ->       'c Bigarray.layout -> 'a array array array -> ('a, 'b, 'c) tval map_file : Unix.file_descr ->       ?pos:int64 ->       ('a, 'b) Bigarray.kind ->       'c Bigarray.layout ->       bool -> int -> int -> int -> ('a, 'b, 'c) tBigarray.Genarray.map_file for more details.val unsafe_get : ('a, 'b, 'c) t -> int -> int -> int -> 'aBigarray.Array3.get, but bounds checking is not always
      performed.val unsafe_set : ('a, 'b, 'c) t -> int -> int -> int -> 'a -> unitBigarray.Array3.set, but bounds checking is not always
      performed.