inject_html
The inject_html filter inserts an HTML snippet immediately before a closing block level tag (</p> </div>) or a closing span tag </span> if they are the last HTML tag in the variable value. If they are not then the HTML snippet is simply appended to the variable value.
This filter is unique to Aptuitiv. It is not part of the core Twig functionality.
{{ post.abstract|inject_html(' <a href="' ~ post.url ~ '">Read more<a>') }}