Not sure if this would be welcome as its kind of an extension...

[DigitalSorceress]

I love parsedown but I really need to be able to have my links use target=_blank on links to external sites

I didn't want to do anything high impact so I added two config options to

$parser->setAllinksInNewWindow(true);

• simply adds target=_blank to ALL links
  and

$parser->setExtLinksInNewWindow(true);

• adds target=_blank to links that start with http or https (so absolute links) but leaves target=_self on links that don't start with that

Thus if you make a link [text](foo) or [text](/foo) etc with setExtLinksInNewWindow true, it would not apply target=_blank but [link](https://evensamesite/foo) would

I totally understand if this is not a feature you want to add due to not being standard part of markdown - I'll keep it in my fork for those interested