Trigger callbacks and events on focus/blur within

[EwanRoycroft]

Description

Adds the onFocusWithin and onBlurWithin functions, and the focusWithin and blurWithin events. These are triggered when focus moved into/out of a parent node.

Consider the following tree:

root
|-- alpha
|   |-- alpha_1
|-- bravo
|   |-- bravo_1

Focus is first assigned to alpha_1. This triggers focusWithin events for alpha and root. When focus moves to bravo_1, a blurWithin event is triggered for alpha, and a focusWithin event is triggered for bravo. No further events are triggered for root as focus remains within it.

Motivation and Context

See #96 for an example of the issue this solves. I did not want to adjust the way activation works as this will break the TAL specification, and may potentially be a breaking change for some projects. Instead, I propose these new events to allow people to track the movement of focus between parents.

Resolves: #96

How Has This Been Tested?

All current tests pass and I have added additional tests for these callbacks.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [x] My change requires a change to the documentation.
• [x] I have updated the documentation accordingly.
• [x] I have read the CONTRIBUTING document.
• [x] I have added tests to cover my changes.
• [x] All new and existing tests passed.

[JohnPaulHarold]

This seems like a fairly sensible proposal, but no activity from any of the core contributors in over half a year. Is this project still active?

[EwanRoycroft]

@JohnPaulHarold I was told by the devs that they are moving to lrud-spatial. As far as I know, this project is effectively deprecated.

[JohnPaulHarold]

@JohnPaulHarold I was told by the devs that they are moving to lrud-spatial. As far as I know, this project is effectively deprecated.

@EwanRoycroft Thank you for the reply. I can't access that repo, probably because I'm not in the BBC github org, but I'll try and keep an eye out for any mention of it releasing to the public.