[maweki]

The html document is potentially infinite, but its finite length is not encoded in the program (css).

One idea is, to have the same program, and if it terminates, it will terminate if you pick a large enough machine. You don't need to "rewrite" the program to use a larger machine.

So in this case the html document is the tape. Potentially infinite, but not in reality. The css program may handle it as infinite.