I'm trying to `include' a HTML document in another document...Is there a way to do this?

Yes, there are several ways to do this. But remember, HTML is not a programming language - it doesn’t have `directives’: it’s a markup language, so trying to compare it to C or Pascal is not going to be very meaningful. SGML already provides the standard way to do this, using an entry in the DocType Declaration for a file: ]> … and then later when you want to include the file … &foo;