Document the role of Ref in broadcasting. (#32645)

* Document the role of Ref in broadcasting.

* replace with a more relevant example

* Update base/refpointer.jl

Co-Authored-By: Matt Bauman <[email protected]>

Author: tpapp

base/refpointer.jl

@@ -16,7 +16,19 @@ it can be written `Ref(a, i)` for creating a reference to the `i`-th element of
 When passed as a `ccall` argument (either as a `Ptr` or `Ref` type), a `Ref` object will be
 converted to a native pointer to the data it references.
 
-There is no invalid (NULL) `Ref` in Julia, but a `C_NULL` instance of `Ptr` can be passed to a `ccall` Ref argument.
+There is no invalid (NULL) `Ref` in Julia, but a `C_NULL` instance of `Ptr` can be passed to
+a `ccall` Ref argument.
+
+# Use in broadcasting
+
+Broadcasting with `Ref(x)` treats `x` as a scalar:
+```jldoctest
+julia> isa.(Ref([1,2,3]), [Array, Dict, Int])
+3-element BitArray{1}:
+ 1
+ 0
+ 0
+```
 """
 Ref