[ Apologies in advance for not distilling this to a minimum example.
I'm not sure how to do so without a bunch of edits in production pages,
and I can't immediately duplicate it in my sandbox. Since I can't figure
out how two pieces of the puzzle are interacting, I don't want to
blindly drop out something that might be related. ]
I have a template
https://en.wikibooks.org/wiki/Template:OpenSCAD_Tutorial/example that
attempts to encapsulate the layout for an example.
It's not terribly complex:
<table class="wikitable" style="border: 2px solid Gold;">
<caption style="text-align:
left;">[[{{BOOKNAME}}/examples/{{{name}}}|Code - {{{name}}}.scad]]</caption>
<tr><td>
{{Pre|{{{content|{{msgnw::{{BOOKNAME}}/examples/{{{name}}}}}}}}}}
</td></tr>
</table>
[[File:{{{name}}}.{{{imgtype|jpg}}}|{{{size|680px}}}]]
<noinclude>{{BookCat}}</noinclude>
The intent is that it's invoked like so:
{{OpenSCAD Tutorial/example|name=a_small_cube}}
to suck in example source text and an example image from separate pages.
It can also be invoked as:
{{OpenSCAD Tutorial/example|name=a_small_cube|content=
cube(10);
}}
to specify the source text in-line.[*]
[*] Yes, I know the header still tries to link to the separate
page. It's still a work in progress.
When I first put it together with the separate-page style, everything
seemed OK. Then somebody wrapped the {{BookCat}} in <noinclude>, and
"{{BookCat}}" started appearing on the final pages. I'm not completely
sure how <noinclude> works, but OK, I can believe that. I started a
conversation with the other editor about why they added the <noinclude>.
Meanwhile, other editors had commented that the
example-in-a-separate-page scheme would be unwieldy. OK, so I went to
back off to the content= style.
And the BookCat problem went away. The BookCat problem is there for the
example-in-separate-page invocation, but not for the in-line invocation.
You can see this at
https://en.wikibooks.org/w/index.php?title=OpenSCAD_Tutorial/Chapter_1&…
. The first example (a_small_cube) uses the in-line style and does not
show {{BookCat}}. The second example
(a_cube_with_different_side_lengths) uses the separate-page style and
shows the {{BookCat}}.
I can't see how those two things can possibly be tied together.