Explicitly call out reverse ranges in : and range docstring (#53626)

base/range.jl

@@ -32,7 +32,7 @@ _colon(::Any, ::Any, start::T, step, stop::T) where {T} =
     (:)(start, [step], stop)
 
 Range operator. `a:b` constructs a range from `a` to `b` with a step size
-equal to 1, which produces:
+equal to +1, which produces:
 
 * a [`UnitRange`](@ref) when `a` and `b` are integers, or
 * a [`StepRange`](@ref) when `a` and `b` are characters, or
@@ -41,6 +41,9 @@ equal to 1, which produces:
 `a:s:b` is similar but uses a step size of `s` (a [`StepRange`](@ref) or
 [`StepRangeLen`](@ref)). See also [`range`](@ref) for more control.
 
+To create a descending range, use `reverse(a:b)` or a negative step size, e.g. `b:-1:a`.
+Otherwise, when `b < a`, an empty range will be constructed and normalized to `a:a-1`.
+
 The operator `:` is also used in indexing to select whole dimensions, e.g. in `A[:, 1]`.
 
 `:` is also used to [`quote`](@ref) code, e.g. `:(x + y) isa Expr` and `:x isa Symbol`.
@@ -66,8 +69,12 @@ Mathematically a range is uniquely determined by any three of `start`, `step`, `
 Valid invocations of range are:
 * Call `range` with any three of `start`, `step`, `stop`, `length`.
 * Call `range` with two of `start`, `stop`, `length`. In this case `step` will be assumed
-  to be one. If both arguments are Integers, a [`UnitRange`](@ref) will be returned.
-* Call `range` with one of `stop` or `length`. `start` and `step` will be assumed to be one.
+  to be positive one. If both arguments are Integers, a [`UnitRange`](@ref) will be returned.
+* Call `range` with one of `stop` or `length`. `start` and `step` will be assumed to be positive one.
+
+To construct a descending range, specify a negative step size, e.g. `range(5, 1; step = -1)` => [5,4,3,2,1]. Otherwise,
+a `stop` value less than the `start` value, with the default `step` of `+1`, constructs an empty range. Empty ranges
+are normalized such that the `stop` is one less than the `start`, e.g. `range(5, 1) == 5:4`.
 
 See Extended Help for additional details on the returned type.
 See also [`logrange`](@ref) for logarithmically spaced points.