Fold YAML front matter

ftplugin/markdown.vim

@@ -22,6 +22,11 @@ endif
 function! MarkdownFold()
   let line = getline(v:lnum)
 
+  " Front matter
+  if v:lnum == 1 && line == '---'
+    return ">20"
+  endif
+
   " Regular headers
   let depth = match(line, '\(^#\+\)\@<=\( .*$\)\@=')
   if depth > 0
@@ -38,6 +43,12 @@ function! MarkdownFold()
     return ">2"
   endif
 
+  " End of front matter
+  let prevline = getline(v:lnum - 1)
+  if (prevline == '...') && (foldlevel(v:lnum-1) == 20)
+    return '>0'
+  endif
+
   return "="
 endfunction