Marking mustache/Jinja-style templates as code blocks

[effigies]

I work with some projects that are mostly markdown, and the pandoc plugin is the best I've found for working with markdown with language fences.

One problem I have though is with projects that use templating engines, for example, mkdocs-macros-plugin uses Jinja2. This is extremely flexible, and ultimately can be any Python code. For example:

{{ MACROS___make_table(["x", "y", "z"]) }}

Due to the triple underscore, everything is bold and italic until the next MACROS___ call:

I've fiddled around with attempting to treat these as code fences, to no avail:

diff --git a/syntax/pandoc.vim b/syntax/pandoc.vim
index 38df7f1..d58a7d8 100644
--- a/syntax/pandoc.vim
+++ b/syntax/pandoc.vim
@@ -450,9 +450,10 @@ syn match pandocTableHeaderWord /\<.\{-}\>/ contained containedin=pandocGridTabl
 " this is here because we can override strikeouts and subscripts
 syn region pandocDelimitedCodeBlock start=/^\(>\s\)\?\z(\([ ]\+\|\t\)\=\~\{3,}\~*\)/ end=/^\z1\~*/ skipnl contains=pandocDelimitedCodeBlockStart,pandocDelimitedCodeBlockEnd keepend
 syn region pandocDelimitedCodeBlock start=/^\(>\s\)\?\z(\([ ]\+\|\t\)\=`\{3,}`*\)/ end=/^\z1`*/ skipnl contains=pandocDelimitedCodeBlockStart,pandocDelimitedCodeBlockEnd keepend
-call s:WithConceal('codeblock_start', 'syn match pandocDelimitedCodeBlockStart /\(\(\_^\n\_^\|\%^\)\(>\s\)\?\( \+\|\t\)\=\)\@<=\(\~\{3,}\~*\|`\{3,}`*\)/ contained containedin=pandocDelimitedCodeBlock nextgroup=pandocDelimitedCodeBlockLanguage', 'conceal cchar='.s:cchars['codelang'])
+syn region pandocDelimitedCodeBlock start=/{{/ end=/}}/ skipnl contains=pandocDelimitedCodeBlockStart,pandocDelimitedCodeBlockEnd keepend
+call s:WithConceal('codeblock_start', 'syn match pandocDelimitedCodeBlockStart /\(\(\_^\n\_^\|\%^\)\(>\s\)\?\( \+\|\t\)\=\)\@<=\(\~\{3,}\~*\|`\{3,}`*\)\|{{/ contained containedin=pandocDelimitedCodeBlock nextgroup=pandocDelimitedCodeBlockLanguage', 'conceal cchar='.s:cchars['codelang'])
 syn match pandocDelimitedCodeBlockLanguage /\(\s\?\)\@<=.\+\(\_$\)\@=/ contained
-call s:WithConceal('codeblock_delim', 'syn match pandocDelimitedCodeBlockEnd /\(`\{3,}`*\|\~\{3,}\~*\)\(\_$\n\(>\s\)\?\_$\)\@=/ contained containedin=pandocDelimitedCodeBlock', 'conceal cchar='.s:cchars['codeend'])
+call s:WithConceal('codeblock_delim', 'syn match pandocDelimitedCodeBlockEnd /\(`\{3,}`*\|\~\{3,}\~*\)\(\_$\n\(>\s\)\?\_$\)\@=\|}}/ contained containedin=pandocDelimitedCodeBlock', 'conceal cchar='.s:cchars['codeend'])
 syn match pandocBlockQuoteinDelimitedCodeBlock '^>' contained containedin=pandocDelimitedCodeBlock
 syn match pandocCodePre /<pre>.\{-}<\/pre>/ skipnl
 syn match pandocCodePre /<code>.\{-}<\/code>/ skipnl

I don't know if this is a feature you're interested in supporting, but if you are able to point me in the right direction to solve the problem for myself, I would appreciate it very much.