Basic concept of spatial navigation

Preconditions

SpatNav Spec is too complicated, so we need to list up the preconditions for the spec.

• The default container is the document element of a browsing context’s document (not limited to the top-level browsing context) or a scroll container.
• The scrollable area is focusable.
• Candidates are focusable elements which are visible within the scrollport of a specific container.

Points to be considered

• Does the spatnav container delegates focus to the element inside it?
• Do candidates need to consider the invisible focusable element within the spatnav container?

Core Features

1. Spatial focus navigation heuristic

• Feature: The basic spatial navigation behavior supported by the browser.

2. Creating container: 'spatial-navigation-contain'

• Feature: Make the elements within a container take higher priority when searching for the best candidate.

• Basically, the element specified with this property isn't focusable. It needs to be specified with tabindex for being a focusable element.

• Issue

  • Do we need 'delegate focus' option for the container?

3. NavigationEvent

• Feature: Fire before the arrow key triggers some behavior (moving the focus, scrolling, nothing).

  • Moving the focus: navbeforefocus
  • Scrolling: navbeforescroll
  • Nothing: navnotarget

• Purpose

  • Cover the edge cases of SpatNav heuristic
    • Using navbeforescroll: Move the focus directly to a candidate without scrolling. (But how?)
  • SpatNav customization
    • Using navnotarget: When there is any candidate at the end of scroll, move the focus to the first element within the spatnav container. (related to the previously proposed "nav-loop")

4. JS API

• Feature: Find the best candidate which will gain the focus.
• Purpose
  • Cover the edge cases of SpatNav heuristic
  • SpatNav Navigation algorithm customization
    • Apply the other spatial focus navigation algorithm. (related to the previously proposed "nav-rule")

Points to be considered

• Is there a way to move the focus directly to the invisible focusable within the scrollable spatanv container?