Set up commentring in the document's YAML metadata region

[krishnakumarg1984]

Unsure if this issue should be filed in the main plugin repo or here.

If the buffer's filetype is set to pandoc, the appropriate vim-pandoc sub-project must set the commentring variable in the appropriate yaml metadata region for the document. This will aid the writer's workflow by integrating with the various commenting plugins (tcomment, commentary etc.)

eg.

---
title: 'Eating Habits'
author: John Doe
date: March 22, 2005
# parallaxBackgroundImage: ./images/leaves_bg.jpg
pandocomatic_:
  use-template:
    - md_to_beamer_basic_pdf
    # - md_to_pptx_basic
    - md_to_revealjs_with_Mathjax
  pandoc:
    incremental: true
    # css:
    # - reveal.js/css/theme/solarized.css
  metadata:
    theme: metropolis
---

This is the yaml-metadata block for the document. I'd like to comment and uncomment various sections eg. the css property. I could just use gcj with tcomment if the plugin sets the yaml codeblock's local commentstring to # and then back to the standard HTML commenting in the rest of the buffer.

[alerque]

I'm not sure where this goes either, or even if it can be done from this end. I know some commenting plugins detect regions of other languages. Others such as nerdcommenter (which I maintain) don't support this at all yet (see issue 17) because it's a really complicated problem.

If file-type plugins such as this one are able to change the commentstring value based on their syntax rules, that might open up a whole realm of things I didn't know was possible.

[fmoralesc]

@alerque It is possible, it is more or less what we do with formatoptions and autoformatting. This is exactly why it would be nice to have an external tool like pandoc give us block metadata, we could do this asynchronously.

[MuhammadSawalhy]

If file-type plugins such as this one are able to change the commentstring value based on their syntax rules, that might open up a whole realm of things I didn't know was possible.

https://github.com/suy/vim-context-commentstring

[alerque]

If you want a whole new realm to open up, I think the answer is this needs to be done using a tree sitter not a syntax rules. Unfortunately Markdown has so far defied anybody to set one up properly.