diff --git a/_posts/coding/2023-05-27-captioning-jekyll-highlighted-code-block.tl b/_posts/coding/2023-05-27-captioning-jekyll-highlighted-code-block.tl
index df23b31..f079764 100644
--- a/_posts/coding/2023-05-27-captioning-jekyll-highlighted-code-block.tl
+++ b/_posts/coding/2023-05-27-captioning-jekyll-highlighted-code-block.tl
@@ -34,8 +34,9 @@ Caption generating code can be freely modified. It can even
 process additional options passed to @{% raw %}{% highlight %}{% endraw %}@ tag.
 Options are only allowed to consist of alphanumeric characters and underscore.
 Passing file path as option requires loosening this restriction. We allow any
-non-blank character, except those used to control option format (options are
-allowed to be expressed as: _name_, _name=value_ and _name="quoted list"_)
+"non-blank character":https://ruby-doc.org/current/Regexp.html, except those
+used to control option format (options are allowed to be expressed as: _name_,
+_name=value_ and _name="quoted list"_)
 
 {% highlight ruby caption=_plugins/highlight-caption-option.rb %}
 module HighlightCaption