HTMX can do the same thing: you can do `hx-trigger="changed delay:500ms"`, and make an endpoint for that component that will do validation, update an error message status area (adding or removing an error as appropriate), and even potentially enable / disable the "submit" button.

It seems to me that the main difference in approach is whether the "source of truth" for the state of the page is on the client or the server. HTMX is designed to be flexible (which is one of TFA's complaints actually), but its primary vision is HATEOAS (Hypertext as the Engine of Application State); which to my understanding of reading HTMX's documentation, is meant to mean that everything important about the client state should be kept on the client; the server should be able to be entirely reactive. What I see skimming through MESH (and data-star.dev) is that the "source of truth" is on the server.

Not an authority in this area, so happy to be corrected on all those points. But I am in the middle of building a dynamic query form using HTMX, trying to design it with HATEOAS principles, so it is something fresh in my mind at any rate.