everypage is made powerful by integrating plugins from creators all over the internet. Plugins allow you to extend the functionality of your page holistically (i.e. not in a particular section).
Here's a quick view of what the plugins look like for our everypage homepage.

The important parts here are that:
type property that defines which plugin is being usedYou should notice that this follows pretty much the same structure as sections.
The rest of the properties (except type) depend on the actual plugin being used. You can see details for each one in the Plugin Directory.