Stax are what most WYSIWYG systems would call Templates. Stax in HAX are a series of HAX element schema's in succession.

Below is a definition for the "example lesson" seen above. This is a larger example, most templates will probably only be a few items. A stack template is like a blox / layout element except the pieces do NOT have to move as a group and they can be deleted. It's more of a shortcut for generating items. The details area describes the element visually in the UI while the subsequent stax  property is an array of HAX element schemas.