How to add a notification in a calendar

There is a calendar standard called hCalendar that implements RFC2445.  Some other keywords of interest are iCal and vCal.  These use the iCalendar file format which is the defacto standard for calendar information interchange.  

You may be able to use PHP to force a download of a file with the ics file suffix.  The client's computer may associate the .ics files with a calendar program.  This file extension is used for calendaring and scheduling information.

The MIME type for iCalendar data is text/calendar.

I've done this in the past with an "add this event to my calendar" link.  The link went to a PHP script and it had a URL parameter giving a key to the calendar entry.  The PHP script used the key to locate the event row in the calendar database table.  It generated an iCalendar object, which is a simple text file like this (thanks, Wikipedia)

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//hacksw/handcal//NONSGML v1.0//EN
BEGIN:VEVENT
UID:uid1@example.com
DTSTAMP:19970714T170000Z
ORGANIZER;CN=John Doe:MAILTO:john.doe@example.com
DTSTART:19970714T170000Z
DTEND:19970715T035959Z
SUMMARY:Bastille Day Party
END:VEVENT
END:VCALENDAR

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If I can find a code example for this, I'll post it here and update these articles about handling date and time in PHP.
https://www.experts-exchange.com/articles/201/Handling-Date-and-Time-in-PHP-and-MySQL-Procedural-Version.html
https://www.experts-exchange.com/articles/20920/Handling-Time-and-Date-in-PHP-and-MySQL-OOP-Version.html

Thank you! Sorry for not having responded eaarlier.
Regards
Lennart