... and of course, in Lisp you can embed other languages in terms of their syntax trees, so the composed language problem goes away. Your HTML just looks like (html (head ...) (body (h1 ...))) or whatever; no "language box for HTML" needed.
That's the point, HTML is just a hobbled lisp with an awkward syntax. If you're building a template engine in a lisp, it's much nicer to just use the native lisp syntax instead.
What happens when you misplace a tag, and it's around 1995, is that browsers somehow parse it anyway without complaining, rendering the page anyway. Users then believe that this is the correct syntax: closing tags is optional, as is the order in which it is done. Twenty years later, you end up with a mess of a situation where every browser has to support not only its own historic buggy behaviors but those of other browsers.
You cannot "misplace" a closing parenthesis, at best you can have too many of them not enough. Of course, you can enclose the wrong amount of material, but to see what is being enclosed, you just need parenthesis matching support in the editor. This is more common than XML tag matching support. E.g.
