Documentation for version v72
Trigger types
Page view

Initialization
The trigger fires before all other triggers fire. Use this trigger to have it fire the tags you want before other triggers.
DOM ready
The trigger fires after the browser has completed processing the HTML code of the page.
The browser has fully loaded the HTML and the DOM tree has been built, but external resources such as <img> images and styles may not have been loaded yet.
Window loaded
The trigger fires after the page has fully loaded, including images, scripts, and other embedded objects.
Page view
The trigger fires when the page begins to load. Used to obtain data only on page impressions.
Click

Click on item
The trigger fires when you click on any page item, including links, images, buttons, etc.