One of the things in HTML5 that caught my eye a while back was the new 'scoped' attribute for style tags. The idea of it is that you can include a style element mid-document, mark it as scoped and its declarations will only apply to the style elements parent element and its child elements. The styles won't affect anything outside this. The biggest problem with bringing in this attribute is that it's not backwards compatible. If you include a style block mid-page, its declarations will be applied to ever element whose selector matches, inside or outside scope. It is anti-progressively enhancable. This means that designers and developers can't start using it until there's enough support. What we need is another of those JS tricks to make it usable.

My first attempt at solving this problem with JS involved generating a unique class, adding it to the parent element and then parsing the style blocks using JSCSSP so that I could rewrite them with the new class to add specificity. This approach only worked for the most basic declarations, unfortunately. The parser worked perfectly but there's a lot of detail in CSS specificity that mean this would be a much larger problem than I thought.

My second attempt involved:

  1. Allowing the style blocks to affect everything on the page (at which point, the elements in-scope look right, those out-of-scope look wrong)
  2. Using JS to read the current computed styles of each element in-scope and copy them to a temporary array
  3. Emptying out the scoped style element (in-scope look wrong, out-of-scope looks right)
  4. Copying the styles back from the temporary array onto each element

This worked great unless you had more than one scoped block – step 1 allowed scoped styles to affect each other.

The current attempt involves temporarily emptying all other scoped styles before taking the computed styles from a block. I'm now just thinking that this method might not work if you have multiple scoped blocks within the same context. Oh well, there's something to fix in the future.

This is where I'm at just now.

Yes, it's a mess, yes the JS is scrappy and yes, it doesn't currently work in IE but I'll get round to that next. It took long enough to get it working in Firefox as there's no simple way to convert a ComputedCSSStyleDeclaration to a string in Mozilla unlike Webkit's implementation of cssText or IE's currentStyle. I might even make it into one of those new-fangled jQuery plugins everyone's using these days.