When you include a file inside a function, remember that it will be executed in its context, which is very likely to break some things for some code. (for example all globals will be undefined without calling global
statement before)
For example, consider you add this to your class xyz:
private function test() {
echo 'test';
}
Now, in the included file you can put:
<?php
$this->test();
Now if you load this file using this class, test
will be outputted.
The question is why do you want to load files with a help of the class and a function and if it's really neccessary.
When a file is included, the code it contains inherits the variable scope of the line on which the include occurs. Any variables available at that line in the calling file will be available within the called file, from that point forward. However, all functions and classes defined in the included file have the global scope.
(https://php.net/manual/en/function.include.php)
(also, about only top part of the page being shown, check the file that is being included, what it really contains; also check for errors in your server log, they will let you more easily spot the issue)