**Feature summary** (what you would like to be able to do and where):
Allow usage of the `filter` CSS property on pages with a content model other than `sanitized-css`. Specifically, in the `style` attribute of elements.
**Use case(s)** (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
I tried to make the Ditto sprite in a userbox at [[https://bulbapedia.bulbagarden.net/wiki/User:Bfdifan2006|bulba:User:Bfdifan2006]] yellow by wrapping it with a div whose `filter` is `hue-rotate(135deg)`, but MediaWiki blocked the property stating it's insecure (by changing it to `/* insecure input */`. I actually commented it out in the wikitext.
**Benefits** (why should this be implemented?):
This could come useful for wikis that are a bit too reluctant to adopt TemplateStyles, and also for users that are a bit confused about the extension's functionality.
I think this was blocked for security reasons when `-ms-filter` was used in Internet Explorer for filters ([[https://docs.microsoft.com/en-us/previous-versions/ms530752(v=vs.85)|more information]]), but the property was deprecated in version 9 and removed from the core in version 10. The browser is going to lose Microsoft support soon due to the success of the Blink-based Microsoft Edge.
It was not a W3C-compatible property, it used a different syntax. However, the W3C-compatible property is safe.