Add docstring for Base.Sort.SMALL_ALGORITHM (#53807)

Co-authored-by: Lilith Orion Hafner <lilithhafner@gmail.com>
Co-authored-by: Steven G. Johnson <stevenj@mit.edu>

base/sort.jl

@@ -812,6 +812,16 @@ Characteristics:
 it is well-suited to small collections but should not be used for large ones.
 """
 const InsertionSort = InsertionSortAlg()
+
+"""
+    SMALL_ALGORITHM
+
+Default sorting algorithm for small arrays.
+
+This is an alias for a simple low-overhead algorithm that does not scale well
+to large arrays, unlike high-overhead recursive algorithms used for larger arrays.
+`SMALL_ALGORITHM` is a good choice for the base case of a recursive algorithm.
+"""
 const SMALL_ALGORITHM = InsertionSortAlg()
 
 function _sort!(v::AbstractVector, ::InsertionSortAlg, o::Ordering, kw)

test/sorting.jl

@@ -12,7 +12,7 @@ using .Main.OffsetArrays
 @testset "Base.Sort docstrings" begin
     undoc = Docs.undocumented_names(Base.Sort)
     @test_broken isempty(undoc)
-    @test undoc == [:Algorithm, :SMALL_ALGORITHM, :SMALL_THRESHOLD, :Sort]
+    @test undoc == [:Algorithm, :SMALL_THRESHOLD, :Sort]
 end
 
 @testset "Order" begin