Brian Kardell

Brian is a Sr Front-End Engineer at The Apollo Education Group. He is one of the co-authors and co-signers of the Extensible Web Manifesto (, and is the chair of the W3C Extensible Web Community Group. He is co-author of HitchJS and a member of the W3C CSS Working Group (JQuery) and generally active in the standards community.

Pandora’s box model

An experiment in containing stylesheet complexity.

This post is part of my personal notes about the benefits currently specified in Shadow DOM, but contentious and held up in committee. We’ll work it out in standards, I’m sure — but given the number of things Shadow DOM was addressing, it may still be several years until we have solutions widely implemented and deployed that solve all of them. This has me doing a lot of thought exercises about what can be done in the meantime. The following reflects one such exercise: specifically, what would it mean to solve just the styling end of this on its own. Warning: it may be mildly crazy.


The Pandora Box

CSS works really well if you can follow good patterns and have nice rich markup. It lets you define broad rules and inherit and override selectively, and if used well it cleanly decouples a separation of concerns — it’s pretty elegant actually.

On the other hand, in the real world, things are often not that simple: until pretty recently, HTML wasn’t especially expressive natively, so we worked around it — many times on our own by adding classes like “article.”  But, there wasn’t a standard. Likewise, our ideas about the patterns we should follow or best practices continues to change as we gain new powers or spend more time with the technology. Of course, there are a vast number of cases where you’ll just go and upgrade your philosophy and be the better for it, but there are a number of times when this just isn’t an option. This is sometimes referred to in standards circles, less colorfully, as “the composition problem.”

When it comes to these sorts of cases, quality and philosophy are inevitably mixed and not entirely in the control of any one team. In these sorts of cases, CSS selectors are kind of like live hand grenades, it’s just way too easy to do damage you didn’t intend to do because it requires a level of coordination of approach which is, for business reasons, highly impractical. And so you try really hard to analyze the problem, get the right select/cascade/descend/inherit/specificity, pull the pin, lob it into the pages and… hope. Frequently, all hell breaks loose. The more you mix it up, the harder it gets to reason about and the more our stylesheets explode in complexity. You’ve opened the proverbial Pandora’s Box.

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