Use extended help for loadmodel! docstring

src/loading.jl

@@ -1,4 +1,8 @@
 loadleaf!(dst, src, err) = dst
+loadleaf!(dst::AbstractArray, src, err) =
+  error("Tried to copy $src into an array destination; this is not allowed.")
+loadleaf!(dst, src::AbstractArray, err) =
+  error("Tried to copy an array to $dst; this is not allowed.")
 function loadleaf!(dst::AbstractArray, src::Bool, err)
   if iszero(src)
     dst .= src
@@ -30,20 +34,12 @@ _bool_tie_check(dst, src) = true
 Copy all the parameters (trainable and non-trainable) from `src` into `dst`.
 
 Recursively walks `dst` and `src` together using [`Functors.children`](@ref),
-and calling `copyto!` on parameter arrays.
-Non-array elements (such as activation functions) are not copied
-and do not need to match between `dst` and `src`.
-Inactive parameters can be encoded by using the boolean value `false` instead of an array.
-If `dst == false` and `src` is an all-zero array, no error will be raised (and no values copied);
-however, attempting to copy a non-zero array to an inactive parameter will throw an error.
-Likewise, copying `src == false` to any `dst` array is valid, but copying `src == true` will error.
-
-Throws an error when:
-- `dst` and `src` do not share the same fields (at any level)
-- the sizes of leaf nodes are mismatched between `dst` and `src`
-- `dst` is a "tied" parameter (i.e. refers to another parameter) and
-  loaded into multiple times with mismatched source values
+and calling `copyto!` on parameter arrays or throwing an error when there is a mismatch.
+Non-array elements (such as activation functions) are not copied and need not match.
+Zero bias vectors and `bias=false` are considered equivalent
+(see extended help for more details).
 
+# Examples
 ```julia
 julia> using Flux: loadmodel!
 
@@ -69,6 +65,22 @@ true
 julia> dst[2].bias == src[2].bias
 true
 ```
+
+# Extended help
+
+Throws an error when:
+- `dst` and `src` do not share the same fields (at any level)
+- the sizes of leaf nodes are mismatched between `dst` and `src`
+- copying non-array values to/from an array parameter
+  (except inactive parameters described below)
+- `dst` is a "tied" parameter (i.e. refers to another parameter) and
+  loaded into multiple times with mismatched source values
+
+Inactive parameters can be encoded by using the boolean value `false` instead of an array.
+If `dst == false` and `src` is an all-zero array, no error will be raised (and no values copied);
+however, attempting to copy a non-zero array to an inactive parameter will throw an error.
+Likewise, copying a `src` value of `false` to any `dst` array is valid,
+but copying a `src` value of `true` will error.
 """
 function loadmodel!(dst, src; cache = Base.IdSet())
   ldsts, _ = functor(dst)