Document download strategy interface

Library/Homebrew/download_strategy.rb

@@ -13,6 +13,23 @@ class AbstractDownloadStrategy
     @meta = resource.specs
   end
 
+  # Download and cache the resource as {#cached_location}.
+  def fetch
+  end
+
+  # Unpack {#cached_location} into the current working directory.
+  def stage
+  end
+
+  # The path to the cached file or directory associated with the resource.
+  def cached_location
+  end
+
+  # Remove {#cached_location} and any other files associated with the resource
+  # from the cache.
+  def clear_cache
+  end
+
   def expand_safe_system_args args
     args = args.dup
     args.each_with_index do |arg, ii|
@@ -34,12 +51,6 @@ class AbstractDownloadStrategy
     safe_system(*expand_safe_system_args(args))
   end
 
-  # All download strategies are expected to implement these methods
-  def fetch; end
-  def stage; end
-  def cached_location; end
-  def clear_cache; end
-
   private
 
   def xzpath