All right, I'm curious if PHP can do (and I'm pretty sure it can) something so that it takes HTML saved as another file and puts it into a PHP script... so like, I have one file called:

htmlheader.html

And three more files:

headerinput.php
headerinput2.php
headerinput3.php

Would it be possible for all three .php files to read the HTML file and insert the HTML code into the PHP script to be read as an 'echo' function? So instead of having to change the header on all three PHP pages (or hundreds if I manage to create that many) I could just change the HTML file and all the other pages would read from that?