doc : may return UnitRange, StepRange, & StepRangeLen (#47670)

Co-authored-by: Sebastian Stock <42280794+sostock@users.noreply.github.com>

base/range.jl

@@ -32,9 +32,14 @@ _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
-of 1 (often a [`UnitRange`](@ref)), and `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.
+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
+* a [`StepRangeLen`](@ref) when `a` and/or `b` are floating-point.
+
+`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.
 
 The operator `:` is also used in indexing to select whole dimensions, e.g. in `A[:, 1]`.
 
@@ -469,9 +474,11 @@ A range `r` where `r[i]` produces values of type `T` (in the first
 form, `T` is deduced automatically), parameterized by a `ref`erence
 value, a `step`, and the `len`gth. By default `ref` is the starting
 value `r[1]`, but alternatively you can supply it as the value of
-`r[offset]` for some other index `1 <= offset <= len`. In conjunction
-with `TwicePrecision` this can be used to implement ranges that are
-free of roundoff error.
+`r[offset]` for some other index `1 <= offset <= len`. The syntax `a:b`
+or `a:b:c`, where any of `a`, `b`, or `c` are floating-point numbers, creates a
+`StepRangeLen`.
+In conjunction with `TwicePrecision` this can be used to implement ranges that
+are free of roundoff error.
 
 !!! compat "Julia 1.7"
     The 4th type parameter `L` requires at least Julia 1.7.