Tabindex is set to 1

I came across this and investigated it. It seems the Addtocalendar Javascript updates the tabindex:

https://addtocalendar.com/atc/1.5/atc.min.js

k.tabIndex=1;

I don't know why it does this.

To add: The issue with the tabindex=1 is that it modifies keyboard navigation such that the first item you end up tabbing to is the "Add to Calendar" button. This breaks accessibility standards for pages that have it.