Demo as in demonstration of what it's capabale of... not demo as trial.
If you'd check through the code in index.php, you'll see that all it does is check to make sure that this isn't the first time the calendar is used (a new setup) and that everything is running ok. Then it checks what you've chosen in the Setup Manager to see if you've disabled the display of demo.php. If you haven't then it includes demo.php and that's what it displays. You're not using demo.php directly, but you'll see that if you modify demo.php in any way, you'll see those changes by going to /calendar/
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