Add LaTeX package from a Lua filter

[bgrenet]

I'd like to know whether it is possible to add a LaTeX package using a Lua filter.

One example of use case: I have a Lua filter that renders some tables using the environment tblr of the LaTeX package tabularray. To make the conversion from markdown to PDF, one needs to put a usepackage{tabularray} in the preamble. Of course, this can be set in the document metadata, or using a custom template. But I'd like that simply saying pandoc document.md --lua-filter=tblr.lua -o document.pdf is enough. Is it possible?

(For this specific case, there may be a workaround. Although I am interested in learning such a workaround, I'm still interested in my original question since I regularly hit this question.)

[jgm]

You can add the usepackage command to a header-includes field in metadata.
Caveat: this won't work well if you're also using --include-in-header on the command line (as this will overwrite anything in metadata).

[bgrenet]

Indeed, I guess that is the way for me. I can live without --include-in-header anyway.