While I agree that it is backwards compatible, I don't agree it's a GUI. It's a document, and HTML is a document standard. The GUI comes from the browser, whose

While I agree that it is backwards compatible, I don't agree it's a GUI. It's a document, and HTML is a document standard. The GUI comes from the browser, whose creator can choose which standard to adhere to, if any. For proof, all you need to do is look at caniuse.com or MDN. Come to think of it, can you say with utmost certainty that today's HTML5 standard will continue to be supported in 25 years' time? That's part of the problem with developing for the modern web - HTML isn't at all composable, because it has no concept of partial views, unless you count iframes. While improvements have been made, it still poorly supports an app model, leaving us to add warts through JavaScript. Although even it is improving, it has plenty of its own warts. In addition to not supporting an app model, the web wasn't built with online payments in mind, has no concept of online identity and no concept of data ownership. The result: dark patterns like tracking cookies, wild growth of payment providers (good and bad), data siphoning, erosion of privacy and the expectancy thereof, and so on.