This are the different possibilities:
can.view.render("url with data", deferred) - returns deferred
can.view.render("only url") - returns renderer functions
can.view("url with data", {}) - returns document fragment
can.view("url with data", deferred) - returns document deferred
can.view("only url") - return renderer function
Consequently a can.view.render renderer function will return an HTML string where a can.view renderer function will return a document fragment.