Update tag-matching regular expressions.

.vim/after/ftplugin/markdown.vim

@@ -13,7 +13,10 @@ function! CompleteTags(findStart, base) abort
     let l:currentLine = getline('.')
     let l:start = col('.') - 1
 
-    while l:start > 0 && l:currentLine[l:start - 1] =~ '[a-zA-Z0-9_\-\:]'
+    " If updating the following regular expression, the tag-matching
+    " regular expressions in "$HOME/.vim/after/syntax/markdown.vim" and
+    " <https://github.com/damiendart/nt> may also require updating.
+    while l:start > 0 && l:currentLine[l:start - 1] =~ '[a-zA-Z0-9/:_-]'
       let l:start -= 1
     endwhile
 

.vim/after/syntax/markdown.vim

@@ -28,10 +28,10 @@ if exists('b:enable_wikilinks_syntax')
 endif
 
 if exists('b:enable_tags_highlighting')
-  " Note: if updating the following regular expressions, the regular
-  " expression used to match tags in <https://github.com/damiendart/nt>
-  " may also require updating.
-  syntax match markdownHashtag ![ '(]#[0-9/:-]*[a-zA-Z][a-zA-Z0-9/:-]*!hs=s+1
-  syntax match markdownHashtag !^#[0-9/:-]*[a-zA-Z][a-zA-Z0-9/:-]*!
+  " If updating the following regular expressions, the tag-matching
+  " regular expressions in "$HOME/.vim/after/ftplugin/markdown.vim" and
+  " <https://github.com/damiendart/nt> may also require updating.
+  syntax match markdownHashtag ![ '(]#[0-9/:_-]*[a-zA-Z][a-zA-Z0-9/:_-]*!hs=s+1
+  syntax match markdownHashtag !^#[0-9/:_-]*[a-zA-Z][a-zA-Z0-9/:_-]*!
   highlight link markdownHashtag Statement
 endif