In Defense of Descendant Selectors and ID Elements

Except when I occasionally update Designing With Web Standards, I quit writing hands-on, nuts-and-bolts stuff about CSS and HTML years ago. Publishing abhors a vacuum: other designers and developers took my place. For the most part, this has been a good thing—for them and for our industry. The best writers about code have always been those who spend 25 hours of every day up their necks in it, as I used to. While folks like me migrate into strategic or supervisory roles (providing us with new places to innovate and new things to write about), a new generation of code crafters is making new discoveries and sharing new teachings. Ah, the magical circle of life.

But amid the oodles of resulting goodness, I find occasional stinkers. Take the notion, now concretizing into dogma, that id should almost never be used because it has “too much specificity,” and that class names are always preferable. Respectfully, I call bunk.

To my knowledge, this notion comes out of Nicole Sullivan’s brilliant Object Oriented CSS, an approach for writing HTML and CSS that is designed to scale on sites containing thousands of pages, created by dozens of front-end developers over a period of years, generally with no rules or style guide in place (at least no rules or style guide until it is too late). On sites like these—sites like Amazon or Facebook that are hosed from the get-go thanks to too many cooks and no master chef—the use of structural id and descendant selectors can be problematic, especially when inept coders try to overwrite an id-based descendant selector rule by creating ever-more-specific descendant selector rules.

In this particular (and rare) circumstance, where dueling developers have added rule after rule to a huge, shapeless style sheet that is more of an archeological artifact than a reasonable example of modern code, Nicole’s admonition to avoid descendant selectors based on id is probably wise. If you have the misfortune to work on a huge, poorly developed site where you will never have permission to refactor the templates and CSS according to common sense and best practices, you may have to rely on class names and avoid descendant selectors and ids.

But under almost any other circumstance, properly used ids with descendant selectors are preferable because more semantic and lighter in bandwidth.

The way I have always advocated using id, it was simply a predecessor to the new elements in HTML5. In 2000, we wrote div id="footer" because we had no footer element, and we wanted to give structural meaning to content that appeared within that div. Today, depending on the browsers and devices people use to access our site, we may well have the option to use the HTML5 footer element instead. But if we can’t use the HTML5 element, there is nothing wrong with using the id.

As for descendant selectors, in a site not designed by 100 monkeys, it is safe to assume that elements within an id’d div or HTML5 element will be visually styled in ways that are compatible, and that those same elements may be styled differently within a differently id’d div or HTML5 element. For instance, paragraphs or list items within a footer may be styled differently than paragraphs or list items within an aside. Paragraphs within a footer will be styled similarly to one another; the same goes for paragraphs within an aside. This is what id (or HTML5 element) and descendant selectors were made for. Giving every paragraph element in the sidebar a classname is not only a needless waste of bandwidth, it’s also bad form.

Say it with me: There is nothing wrong with id when it is used appropriately (semantically, structurally, sparingly). There is plenty wrong with the notion that class is always preferable to descendant selectors and semantic, structural ids.

Please understand: I’m not disparaging my friend Nicole Sullivan’s Object Oriented CSS as an approach to otherwise unmanageable websites. No more would I disparage a steam shovel for cleaning up a disaster site. I just wouldn’t use it to clean my room.

I’ll be discussing code and all kinds of other things webbish with Chris Coyier and Dave Rupert on the Shoptalk podcast today. Meanwhile, let me know what you think. And don’t forget November 30th is the sixth international celebration of Blue Beanie Day in support of web standards. Wherever you may stand on the great id debate, please stand with me and thousands of others this November 30th.