site.static_files is only available in the latest development version of Jekyll.

Ref: #2075

site/docs/plugins.md

@@ -73,6 +73,7 @@ instances of
 and are available via `site.pages`. Static files become instances of
 [`Jekyll::StaticFile`]({{ site.repository }}/blob/master/lib/jekyll/static_file.rb)
 and are available via `site.static_files`. See
+[the Variables documentation page](../installation/) and
 [`Jekyll::Site`]({{ site.repository }}/blob/master/lib/jekyll/site.rb)
 for more details.
 

site/docs/variables.md

@@ -119,6 +119,9 @@ following is a reference of the available data.
         A list of all static files (i.e. files not processed by Jekyll's
         converters or the Liquid renderer). Each file has three properties:
         <code>path</code>, <code>modified_time</code> and <code>extname</code>.
+        <strong>Note: this is only available in <a
+        href="../installation/">the latest development
+        version.</a></strong>
 
       </p></td>
     </tr>