planet4-master-theme/assets/src/js/external_links.js
planet4-master-theme/assets/src/js/pdf_icon.js

setupExternalLinks() and setupPDFIcon() add an icon to external links and a target _blank for external links.

The icon might be manageable in CSS (minus tricks to find for images in anchors).
The automatic _blank target is in discussion:

• in design system https://docs.google.com/presentation/d/1uZqqMNUvOSJiqo7aZgPfeikMn7ASOkJn_IhZkd2JulE/edit#slide=id.ga5821adf34_1_269
• in https://jira.greenpeace.org/browse/PLANET-4334

External links could depend on a list of allowed domains considered as "internal".

External links and PDF links icons (pdf_icons.js) are added in a different way, we could try to unify the method.

• CSS: :before rule depending on href attribute content
• JS: toggle specific class depending on href content / append inline SVG