The HTMLLabelElement.htmlFor property reflects the value of the for content property.

The :empty selector refers only to child nodes, not input values. [value=""] does work; but only for the initial state. This is because a node's value attribute (that CSS sees), is not the same as the node's value property (Changed by the user or DOM javascript, and submitted as form data).

I'm looking at https://html.spec.whatwg.org/#attributes-3 right now, and it seems that there are a few others that ought to be boolean but are not currently in this list: allowpaymentrequest, formnovalidate, hidden (is on the original list in the master branch), itemscope, nomodule, and playsinline.

Svelte currently has no opinion as to what you store in an exported class prop of a component. It will not necessarily be used a class attribute.

If you used browser JS DOM APIs (that have nothing to do with React itself), you know they don’t automatically update attributes