I am a newbie in Odoo and I am seeing that in several models, in some functions there is a return at the end, and it uses to be a dictionary with some predefined values, like for example, type (this one uses to be in everyone).

E.G.:

...

datas = {
   'model': 'account.journal',
   'print_by': print_by,
   'sort_selection': wiz_form.sort_selection,
   'target_move': wiz_form.target_move,
   'display_currency': wiz_form.amount_currency,
   'group_entries': wiz_form.group_entries,
}

return {
   'type': 'ir.actions.report.xml',
   'report_name': 'nov.account.journal.xls',
   'datas': datas,
}

Where can I find the meaning of those attributes? Or there are not predefined and come from an inheritance? Where are they going to?