What happens inside render()?
Notes made when preparing to write my own output format

https://github.com/rstudio/rmarkdown/blame/master/R/render.R

1. knitr::spin(spin_input, knit = FALSE, envir = envir, format = "Rmd")
   line 397

   Only thought here is that default metadata is added unconditionally,
   so I will need to find a way to make sure that is ignored (by having
   user metadata elsewhere in the file) or removed.

   I suppose I will still be including my own frontmatter, in order to
   specify the output format. This could be a good reason to do so via
   YAML instead of in the render() call.

2. YAML front matter is read
   line 420

   Seems pretty boring / irrelevant?

3. output format is read from YAML, if wasn't specified in the call
   line 461

   Seems pretty important but unless I start doing something with options
   doesn't seem to affect me.

4. pandoc_to is set
   line 469

   Determined from the output format: `output_format$pandoc$to`

5. output_format$intermediates_generator is called
   line 502

   Seems irrelevant to me but this is my first chance to do something via
   the custom output format.

6. pre_knit handler is called
   line 532

   Chance to act on the input file, which at this point is the Rmd output of
   spin(knit = FALSE).

7. knitr options and hooks are set
   line 615

   Calls to knitr::opts_knit$set(), knitr::opts_chunk$set().
   I'd need to figure out how to the the tidyverse_quiet R option.

8. Main knit
   line 740

9. post_knit handler is called
   line 748

   Well, this is what the comment says, but the code seems a bit surprising. I
   think it's more accurate to say we're registering a post_knit handler.

10. pre-processor
    line 819

    Again, feels like we're registering a pre-processor.

11. Call pandoc
    line 890

    output_format$pandoc$args is a very important argument

12. Call post processor
    line 949
