templates/fragments/menu_files/en.html is set up not to display some files:
<div
class="files"
xmlns:petal="http://purl.org/petal/1.0/"
petal:condition="true: self/components_list --file"
>
<h2>
<a
xml:lang="en"
lang="en"
dir="ltr"
name="files"
id="files"
>
Files
</a>
</h2>
<div
petal:define="File_Loop self/components_list --file;"
petal:repeat="file File_Loop"
petal:omit-tag=""
>
<p
petal:attributes="class string:file-${file/extension}"
class="file-file"
petal:condition="true: file/title;
false: file/name_is --style.css;
false: file/name_is --favicon.ico;
false: file/name_is --script.js;"
>
<a
href="http://example.com/"
rel="dc:hasPart"
petal:content="file/title"
petal:attributes="href file/uri"
>
File Title
</a>
</p>
</div>
</div>
However the problem with this is that if there are only the named files attached to a page then an empty box is generated.
MKDoc-1.8 solution
This site is running MKDoc 1.8 and it doesn't have this bug… there is a file attached to this page: http://www.mkdoc.org.archived.website/bugs/stable/normal/file-listing-box/favicon.ico
This is because components can be excluded by name using the --exclude parameter in 1.8