There are four(4) types of build-in PHP functions to access an External file (.html or .php) and these are as follows:

include();

include_once(); 

       will post an Error message when any Error had been encountered, but will still continue

require();

require_once(); 

       will Halt the script when any Error had occured

  ex.: 

  < ?php

  # set page title and

  # include the html

  $page_title = 'Calendar Form';

  include('./header.inc');

  # a function declaration

  function make_pull(){

        # some code goes here

         . . .

  }

  echo '< form action="',   'dateform.php"',   'method="post">';

  make_pull();

  echo '</form>';

  include('./footer.inc');'

  ?>