rand() function documentation suggests an inclusive upper bound of 1.0

 The rand() function in PySpark, Spark, and R is documented as drawing from U[0.0, 1.0]. This suggests an inclusive upper bound, and can be confusing (i.e for a distribution written as `X ~ U(a, b)`, x can be a or b, so writing `U[0.0, 1.0]` suggests the value returned could include 1.0). The function itself uses Rand(), which is documented  as having a result in the range [0, 1).