Document using custom loaders in LOAD_PATH

base/initdefs.jl

@@ -30,7 +30,19 @@ isinteractive() = (is_interactive::Bool)
 """
     LOAD_PATH
 
-An array of paths (as strings) where the `require` function looks for code.
+An array of paths as strings or custom loader objects for the `require`
+function and `using` and `import` statements to consider when loading
+code. To create a custom loader type, define the type and then add
+appropriate methods to the `Base.load_hook` function with the following
+signature:
+
+    Base.load_hook(loader::Loader, name::String, found::Any)
+
+The `loader` argument is the current value in `LOAD_PATH`, `name` is the
+name of the module to load, and `found` is the path of any previously
+found code to provide `name`. If no provider has been found earlier in
+`LOAD_PATH` then the value of `found` will be `nothing`. Custom loader
+functionality is experimental and may break or change in Julia 1.0.
 """
 const LOAD_PATH = Any[]
 const LOAD_CACHE_PATH = String[]