The <object> tag appears to include/embed other html pages.
An embedded HTML page:
<object data="snippet.html" width="500" height="200"></object>
An embedded HTML page:
<object data="snippet.html" width="500" height="200"></object>
That said - it does appear encapsulated, much like an iframe - css doesn't take, etc. so though more "pure" HTML I'd argue doesn't fulfill the spirit of "include"?