With WordPress 6.9, numerous legacy features that were used to support Internet Explorer have been removed. All versions of Internet Explorer have been unsupported in WordPress since version 5.8, released in July 2021. These changes continue the process of removing code that existed only to provide support for these browsers.
Removed Support for IE Conditional Scripts and Styles
Conditional comment support was added for scripts in WordPress 4.2, and for styles sometime around version 2.6.0, but was made more easily available in WordPress 3.6.
Conditional comments were a mechanism to pass scripts and styles for specific versions of IE. The last browser to support conditional comments in any way was IE9, which has been out of support by WordPress since version 4.8. No supported browser uses scripts or styles provided within conditional comments, treating them the same as any other commented code.
The feature has been removed, and using the ‘conditional’ argument will throw a deprecation notice (“IE conditional comments are ignored by all supported browsers.”) if WP_DEBUG is set to true.
Any style or script currently loaded using conditional arguments will be ignored, as will any dependencies of those styles or scripts if they are not already required by another script or style.
IE Conditional scripts and styles were removed in core ticket #63821.
Updates to bundled themes
All bundled themes that used conditional comments have been updated to remove usages of conditional comments and CSS Cascading Style Sheets. syntax only used to support Internet Explorer.
CSS and JS JavaScript, a web scripting language typically executed in the browser. Often used for advanced user interfaces and behaviors. files that were only required conditionally remain in place as blank files, containing only comments to indicate when the related support was removed.
Conditional comments were removed from bundled themes in #58836.
IE Compatibility Removals
Compatibility scripts were removed from the Media Elements instantiation process in #63471.
#62128 removed IE-specific hacks and EOT file rules from the Genericons stylesheet for four bundled themes, from Twenty Thirteen to Twenty Sixteen.
Acknowledgements
Props to @jorbin, @westonruter, @jonsurrell and @sabernhardt for reviewing this post.
#6-9, #dev-notes, #dev-notes-6-9
