An .assf file can just contain normal html with no extra markup.
So long as the file does not contain the magic <% starter tag or <[, it should just render as normal HTML.
There will be a little bit of overhead as the .assf file is compiled, and every call to the .assf page will cause the page to be generated by a tcl call.
This is analagous to rendering a static HTML file through the PHP engine. It works, but isn't the most effecient way of rendering static HTML.
<html>
<title> A simple .assf file </title>
<body> Hello World </body>
</html>