What is the “explicit navigation model” of HDML?
The navigation model in HDML is optimized for super-small displays (e.g. 4×20 characters) which do not have a lot of screen space to provide context for the user in the form of “Prev” and “Next” buttons or a pull-down menu of the history. To help prevent the user from “getting lost”, the HDML navigation model emphasizes predictability, and determinism by providing explicit control over the navigational UI of the user agent. The HDML user-interface metaphor is based on “cards” that the user displays and/or interacts with. The navigation model is similar to the HTML model in that there is a notion of moving “forward” and “back”. “Forward” usually means display the next card, and “back” usually means show me the previous card. When building an application interface using small cards, a number of problems arise using a simple history model. For example, if the URL of a card has a side-effect when downloaded from a server, it could be a bad thing for the user to move back to the previous ca
