'mediawiki.skinning.content.externallinks' is an opinionated CSS styling module that should not be part of MediaWiki core, but skin-specific!
Current usage: https://codesearch.wmcloud.org/search/?q=content.externallinks&i=nope&files=&repos=
It is opinionated in comparison to other core HTML element styling modules, to provide out of the box styling for some protocols, file-types etc. Its former most important use cases, like styling HTTPS links and links that open in other software, most importantly PDF files, have lost their importance in current times.
It features a number of problematic issues:
- These opinionated styles should be skin-specific
- It's not well-maintained, which is a result of it not being skin-specific
- It features some protocols, and some file types, but these haven't been updated
- Icons are non-HiDPI-ready
- Icons are largely outdated and don't follow any style guidelines
- Icon distances are set in px via padding which make them not scale properly when user increases browser font size, hence makes it an accessibility issue