Lua filters for title/subtitle appearance?

[helloitsclayton]

Apologies if this has been answered somewhere, but I've been searching around for a few days and haven't managed to find anything.

I'm wondering if it is possible to set up a Lua filter to affect the appearance of the title and subtitle of a document when going from markdown to docx (not the metadata itself). I'm essentially hoping to prevent them from appearing in the resulting docx file altogether, as the printed final document will have a separate title/cover page added, so just adjusting the docx template settings wouldn't work.

[alerque]

Filters are for changing the content of the document tree (AST) not for appearances. The template controls appearance.

That being said you're specifically asking about having them "not appear" at all. Just use a Lua filter and remove the title and subtitle completely. Then they will not appear. There isn't really a sane way to make something like that be in the document contents but invisible anyway.

[bpj]

It depends on how the title and subtitle are expressed in the source. If you use the Pandoc Markdown title metadata field it is very easy: all.you need is to create a Lua filter with

function Pandoc (doc)
  doc.meta.title = nil
  return doc
end

If the title are regular headings or paragraphs you will have to rely on heuristics like identifiers, classes or other attributes, or position in the document.

What format is your source in, and what do the title and subtitle look like in the source?

[helloitsclayton]

I'm using Pandoc flavored markdown, and the title/subtitle are in a separate YAML metadata file.

I did know that I can use Lua filters to affect the metadata, but I was hoping/assuming there'd be a way to affect the title's being printed to the output doc without actually deleting metadata in the process. But it seems like that might not be the case?

[alerque]

You can do that, but it would involve changing the DOCX template file used as a reference for creating the document. You can ask Pandoc to dump the template file it has built in, make your changes to it (delete the place holder for a title), then ask it to use your modified version as a template.

[bpj]

I did know that I can use Lua filters to affect the metadata, but I was hoping/assuming there'd be a way to affect the title's being printed to the output doc without actually deleting metadata in the process. But it seems like that might not be the case?

Note that the metadata are not deleted from the source or the metadata file. They are only deleted from what the docx writer (and any subsequent filters) "see" in that particular run of pandoc.

[helloitsclayton]

@bpj You're right, of course. It's just the librarian in me that hates to see content and metadata mixing in any way.

[HeirOfNorton]

OpenXML format is pretty complicated, but it's pretty easy to edit the default template just to remove the title and subtitle. Right at the top of the template is this block:

$if(title)$
    <w:p>
      <w:pPr>
        <w:pStyle w:val="$title-style-id$" />
      </w:pPr>
      $title$
    </w:p>
$endif$
$if(subtitle)$
    <w:p>
      <w:pPr>
        <w:pStyle w:val="$subtitle-style-id$" />
      </w:pPr>
      $subtitle$
    </w:p>
$endif$

Delete that (and any other blocks you don't need, but make sure to keep the XML at the top and bottom, as well as $body$ and $sectpr$ or the docx will be corrupt). Save the file, and then reference the new temple with --template=<mynewtemplate.openxml>, and that should remove the title and subtitle from the o utput while still keeping them in the metadata.

[helloitsclayton]

Oh, this looks promising! Is there any way to access additional metadata beyond title and subtitle in those if statements? For instance, if I include "hideTitle" metadata variable in my YAML file could I then use that to do something like $if(title and not hideTitle)$?

[HeirOfNorton]

Kind of. You can access any metadata variable in the template. Note, though, that Pandoc's template language is pretty basic compared to something like Jinja or Handlebars. There is no equivalent to and or not, $if(variable)$ only checks for the existence and "truth" of the variable, so something like what you suggest will need to be built up from more primitive parts. One way to fake if not is to check for the variable, but then immediately have an else clause, so the contents are only output if the variable is absent or false. Something like this:

$if(title)$
$if(hideTitle)$
$else$
...
$endif$
$endif$

[helloitsclayton]

Thanks, @HeirOfNorton, I believe this is the best way of implementing the functionality I'm looking for.