"Includes" functionality is considered to be server-side, i.e. handled outside of the web browser. HTML is client-side, and really just a markup syntax, not a programming language. As the article says, the problem is a solved one. The "includes" issue is how every web design student learns about PHP. In most CMSes, "includes" become "template partials" and are one of the first things explained in the documentation. T…
That's not an argument that client-side includes shouldn't happen. In fact HTML already has worse versions of this via frames and iframes. A client-side equivalent of a server-side include fits naturally into what people do with HTML.