Just a thought....
Break up your code into sections. Let's say you have a header, content and footer. Then create a page (index.php for this example) and do this...
<?
require("header.html");
require("content.html");
require("footer.html");
?>
Next question...suppose you want to include some standard stuff in the content.html page, then you could embed php require statements in that, maybe for buttons in a left column of a table.
Again...just a thought. I am new to this, but the above works for me. It also seems to work fine if you have other file extensions, not just html (for instance, .txt files).