Hi Vladislav-S, this should really go to stack overflow, but the deal with
data is this: anything that is passed to the
render method of a module (to render a template) becomes a property of
data in the template.
The reason you can't find an exhaustive list is that it depends on the page you're on. A pieces-page will have
data.pieces, a regular page won't.
That being said, some properties of data are present all or most of the time, such as
data.page (except in places like /login that are not pages in the tree) and
data.user, and it would be helpful for us to document these clearly in one place.