XHP templates in Hack do wind up looking a lot like JSX (which is probably not coincidental).. Each tag is a class with a render function that returns an XML node. Here is an example base document template[0] showing what that looks like. Obviously, PHP templates can accomplish the same thing, it just takes more work and more dependencies to magic away the noise.

But with XML as a native data structure you can do things like typehint a tag:

    public function setTitle(:document:base $base, string $title): void 
    {
        $base->setAttribute("pagetitle", $title);
    }

[0]https://pastebin.com/m54VDwNY