First version.

JS/Script.js

@@ -0,0 +1,26 @@
+function includeHTML() {
+  var z, i, elmnt, file, xhttp;
+
+  console.log("Including HTML.")
+
+  z = document.getElementsByTagName("*");
+  for (i = 0; i < z.length; i++) {
+    elmnt = z[i];
+
+    file = elmnt.getAttribute("include");
+    if (file) {
+      xhttp = new XMLHttpRequest();
+      xhttp.onreadystatechange = function() {
+        if (this.readyState == 4) {
+          if (this.status == 200) {elmnt.innerHTML = this.responseText;}
+          if (this.status == 404) {elmnt.innerHTML = "Page not found.";}
+          elmnt.removeAttribute("include");
+          includeHTML();
+        }
+      }
+      xhttp.open("GET", file, true);
+      xhttp.send();
+      return;
+    }
+  }
+}