message: Update docstring for keras.backend.std.
diff: @@ -2080,16 +2080,22 @@ def var(x, axis=None, keepdims=False):
  def std(x, axis=None, keepdims=False):
  """Standard deviation of a tensor, alongside the specified axis.
  + It is an alias to `tf.math.reduce_std`.
  +
  Arguments:
  - x: A tensor or variable.
  - axis: An integer, the axis to compute the standard deviation.
  + x: A tensor or variable. It should have numerical dtypes. Boolean type
  + inputs will be converted to float.
  + axis: An integer, the axis to compute the standard deviation. If `None`
  + (the default), reduces all dimensions. Must be in the range
  + `[-rank(x), rank(x))`.
  keepdims: A boolean, whether to keep the dimensions or not.
  If `keepdims` is `False`, the rank of the tensor is reduced
  - by 1. If `keepdims` is `True`,
  - the reduced dimension is retained with length 1.
  + by 1. If `keepdims` is `True`, the reduced dimension is retained with
  + length 1.
  Returns:
  - A tensor with the standard deviation of elements of `x`.
  + A tensor with the standard deviation of elements of `x` with same dtype.
  + Boolean type input will be converted to float.
  """
  if x.dtype.base_dtype == dtypes_module.bool:
  x = math_ops.cast(x, floatx())
  