I believe we could have an issue in how we parse format and triage between supported Markdown variants and what we call modifiers (e.g `pdf+draft` and `pdf+final`). 

This is what we get when running the command above 
````
> quarto render doc.qmd --to docx+native_numbering

processing file: doc.qmd

output file: doc.knit.md

pandoc
  to: docx
  output-file: doc.docx
  default-image-extension: png

metadata
  title: test

Output created: doc.docx
````

No `native_numbering` in the `to` field for `pandoc`

From debugging within VSCode it seems we are seing `docx+native_numbering` not as the `+native_numbering` variants and then build the wrong format string. 

Talking about this part of the code 
https://github.com/quarto-dev/quarto-cli/blob/main/src/core/pandoc/pandoc-formats.ts#L171-L216

called 
https://github.com/quarto-dev/quarto-cli/blob/main/src/core/pandoc/pandoc-formats.ts#L171-L12

I feel something is not right there but not sure as it seems the list to detect variants was built on the Markdown format supported ones. 
https://github.com/quarto-dev/quarto-cli/blob/main/src/core/pandoc/pandoc-formats.ts#L218

@dragonstyle knows better this part of the code.  If this is confirmed, we should transfer to an issue probably

Note that doing 
````yaml
format: docx
variant: +native_numbering
````

seems to correctly pass the variant as quarto command prints 
````
pandoc 
  to: docx+native_numbering
````

but we document variant only for `markdown` output. 

Hope it helps

_Originally posted by @cderv in https://github.com/quarto-dev/quarto-cli/discussions/4020#discussioncomment-4732171_
    
dragonstyle
2023-01-24T15:02:57Z
cderv
v1.4
open
Parsing format string with Pandoc's extensions 
https://github.com/quarto-dev/quarto-cli/issues/4080