[wabain]

Did XHTML ever allow styling with XPath, or is it just used for jQuery-style element selection? My uneducated impression was that for performance reasons browser devs were rejecting even more restricted backwards-lookup and nesting selectors for styling.

I've encountered some uses of XPath to validate the semantics of XML data models (this kind of thing still has mindshare in some places - network devices for instance https://tools.ietf.org/html/rfc7950#section-7.21.5 ) and I've come to the conclusion that wanting XPath is usually a danger sign. It's helpful for manipulating content you can't control, but that leads to people designing interfaces and models that are too difficult to work with downstream. In document display settings that manifests as a content vs. presentation mentality where you have to write byzantine queries to wrestle data into reasonable output. In configuration use cases I've seen it lead to interfaces that claim way more general edit operations than the implementation can actually pull off, as people struggle to specify XPath-based constraints to make it tractable. It's much better if at all possible to have some kind of scripted layer to do transformations than to try to manipulate a general presentable-cum-semantic data tree.

On the XHTML vs HTML5 side, React at least does a good job warning you if you're trying to render something that violates DOM nesting (out of necessity as much as anything, since it will need to operate on the generated tree).

[Camillo]

You could use XPath in an XSLT stylesheet to style XHTML.

[toyg]

In fact, you pretty much had to...