I’d like to share with you a script I’ve found on the MadCap Forums that you can use to open external links (<a href>) by default in a new target frame.
To do so, you can add the script below to the body part of your page layout (.flmsp):
<script type="text/javascript">/*<![CDATA[*/ $("a[href^='https://']").attr('target="_blank"');/*]]>*/</script>
Note that I’ve slightly modified the original script suggested at https://forums.madcapsoftware.com to fit my needs (http to https and the inverted commas in the attribute).
You can also replace the attribute value (“_blank” in this case) by:
_parent _self _top
And apply any other attribute supported by <a>. For a complete list, see: w3schools.com/tags/tag_a.asp