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.
• Focusable elements in spatnav
  • The browsing context is focusable.
  • The scrollable area is focusable.
  • The negative integer value of tabindex makes the element be omitted from the spatial navigation order.
    • There are several elements which the tabindex focus flag be set: (https://html.spec.whatwg.org/multipage/interaction.html#specially-focusable)
    • The element with tabindex=-1 is omitted from the spatial navigation order but, if there is a focusable child element, it will be included in the spatial navigation order.
• 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?

Terminology

• startingPoint: The currently focused **area **of a top-level browsing context. (Searching origin)
  • From the startingPoint, spatnav finds the best candidate depends on the direction.
  • It can be a node or a position.
• spatial navigation starting point: The starting point that is specified by UA.
  • For example, if UA defines clicking the element can change the starting point, then the clicked element becomes
• spatial navigation focus container(a.k.a. spatnav container): The group of focusable elements which can navigate via spatnav

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?