Show the code for sample generator first [skip ci]

docs/_docs/plugins/generators.md

@@ -44,6 +44,20 @@ This is a more complex generator that generates new pages:
 
 ```ruby
 module Jekyll
+  class CategoryPageGenerator < Generator
+    safe true
+
+    def generate(site)
+      if site.layouts.key? 'category_index'
+        dir = site.config['category_dir'] || 'categories'
+        site.categories.each_key do |category|
+          site.pages << CategoryPage.new(site, site.source, File.join(dir, category), category)
+        end
+      end
+    end
+  end
+
+  # A Page subclass used in the `CategoryPageGenerator`
   class CategoryPage < Page
     def initialize(site, base, dir, category)
       @site = site
@@ -59,19 +73,6 @@ module Jekyll
       self.data['title'] = "#{category_title_prefix}#{category}"
     end
   end
-
-  class CategoryPageGenerator < Generator
-    safe true
-
-    def generate(site)
-      if site.layouts.key? 'category_index'
-        dir = site.config['category_dir'] || 'categories'
-        site.categories.each_key do |category|
-          site.pages << CategoryPage.new(site, site.source, File.join(dir, category), category)
-        end
-      end
-    end
-  end
 end
 ```