Mobile design/Wikipedia navigation/Back behavior

This page is a whiteboard for discussion of the back/forward behavior in the new navigation UI. It is also intended to outline all of the expected behavior to aid in implementation.

General principles
At its core, back needs to achieve some basic objectives, which can be summarized as:


 * providing a quick and simple method of going back to an article from any context, such as a menu or submenu
 * providing a simple way to re-trace steps in a detailed way, as in a breadcrumb trail
 * providing a way to cancel some actions, such as typing or navigating to a place that was not desired (such as a language version)

These objectives can be at odds, since the first objective includes a focus on speed and convenience.

From an implementation perspective, this boils down to defining what are the steps in a navigation path. To achieve both objectives, there needs to be a balance between defining many elements as steps, and defining too few.

Defining an article as a step is not enough, since there are potential states of the page, based on the following variables:


 * Action bar showing or not showing
 * section(s) closed or not closed
 * position on the page
 * language

There is also an issue of user expectations, which differ between browser and apps. These differences will be noted in the sections below.