- Apply an animation (or other style) to any CSS styles that specify "text-decoration: blink".
- Specify what colour to use when a CSS rule specifies "background" as the colour name.
- Make all transitions (or animations) twice as fast or twice as slow.
- Prevent certain CSS commands from being used entirely, or change their meaning to a different command.
- Select elements by the CSS rules that the document applies to them (even if those CSS rules are disabled, and even if class names are unpredictable).
- Define exactly how big a "in" or "px" or whatever unit is.
While it sounds like it would make browsers more complex, I think it would actually reduce complexity, because the browser would not need even more programming capability and APIs just to enable web developers to create these kind of features themselves in a thousand variations of Javascript that adds bloat to every connection and slows down end user devices.
And, yes, it would reduce complexity in the ways you specified, in addition to improving efficiency and allowing the user more control, and these are good things to have.
Maybe someone will make a web browser program that can do these kind of things.
Well, more features in web apps isn't what I want; it is instead more and better features in the browser itself, such as:
- User stylesheets and user scripts.
- Ability to save and recall form data using local files.
- Ability to load animated GIF/PNG as videos.
- Request/response overriding (this can also be used to add the Do Not Track header).
- ARIA view (even for display on screen, not only for visually impaired).
- Better keyboard commands.
- Table of contents view (displaying the list of <h1>, <h2>, etc).
- Developer console (which I think newest versions of Chrome and Firefox already have, anyways).