Use callout without custom Jekyll plugin.

docs/4.0/components/buttons.md

@@ -18,8 +18,7 @@ Bootstrap includes several predefined button styles, each serving its own semant
 <button type="button" class="btn btn-link">Link</button>
 {% endexample %}
 
-{% capture callout-include %}{% include callout-warning-color-assistive-technologies.md %}{% endcapture %}
-{{ callout-include | markdownify }}
+{% include callout-warning-color-assistive-technologies.md %}
 
 ## Button tags
 
@@ -94,11 +93,12 @@ Disabled buttons using the `<a>` element behave a bit different:
 <a href="#" class="btn btn-secondary btn-lg disabled" tabindex="-1" role="button" aria-disabled="true">Link</a>
 {% endexample %}
 
-{% callout warning %}
+{% capture callout %}
 ##### Link functionality caveat
 
 The `.disabled` class uses `pointer-events: none` to try to disable the link functionality of `<a>`s, but that CSS property is not yet standardized. In addition, even in browsers that do support `pointer-events: none`, keyboard navigation remains unaffected, meaning that sighted keyboard users and users of assistive technologies will still be able to activate these links. So to be safe, add a `tabindex="-1"` attribute on these links (to prevent them from receiving keyboard focus) and use custom JavaScript to disable their functionality.
-{% endcallout %}
+{% endcapture %}
+{% include callout.html content=callout type="warning" %}
 
 ## Button plugin