We've quietly kept the .htaccess for the core site so that *all* files are parsed as if they were .shtml. The only disadvantage to this approach we've seen is that the JavaScript document.lastModified property is inaccurately passed in the http header, leading one browser to think the current date/time is the value and another to see it as a fixed date in 1970. This is easily resolved by not using that value and inserting it with SSIs, which grab that value directly from the Unix server's file structure.

SSIs also handle the matter of compartmentalizing and reusing boilerplate page elements, the way that framesets used to. By reducing these sections to includes, they can be edited (and sites updated) all at once.