ckeditor/ckeditor5-engine

<style>
    .unsafe-link {
        padding: 0 2px;
        outline: 2px dashed red;
        background: #ffff00;
    }
</style>

<div id="snippet-link-unsafe-classes">
    <p>All links in this <a href="https://ckeditor.com">editor</a> that do not use the <a href="http://developer.mozilla.org/en-US/docs/Glossary/https">HTTPS</a> protocol
    have a custom <code>.unsafe-link</code> CSS <a href="http://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes/class">class</a> that marks them red.</p>
    <p>Edit the URL of the links using "http://" or "https://" to see them marked as "safe" or "unsafe".</p>
</div>