DRAFT: Data navigator research

[c-lamoureux]

This branch contains proof of concept behavior, code is poorly written but conceptually allows us to meet the feature requirements. Major cleanup of code required before merge.

Requirements:
TAB to navigate to the chart

Navigator enter button appears on the center of the chart with user friendly text

In all cases:

• ENTER drills in a layer of depth.
• ESC goes up a layer.
• Arrow Right and Down share the same behavior.
• Arrow Left and Up share the same behavior.

ENTER enters the chart which has this navigation tree structure:
Axis (one for every axis):

• Initial focus is on the entire axis and it's title/labels.
• ENTER focuses a visible axis label.
• Arrow keys navigate between labels on the axis.
• ESC returns you to the whole axis focus
• Axis label focus triggers highlight of connected bars when relevant.

Legend:

• Initial focus is on the entire legend including the title/legend items.
• ENTER focuses the first legend item symbod+label(s)
• Arrow keys navigate between legend items
• ESC returns to the whole legend focus

Bar Chart Content:

• Initial focus is on the chart content (within the axes)
• ENTER focuses the first Bar
• Arrow keys navigate between the bars in sequence
• Navigation ends at the last bar (not circular)
• In a stacked bar, first focus is on the stack, ENTER again to focus the individual bars within a stack.
• In a stacked bar, arrow navigation in the inner bar stack can still navigate between stacks.
• Focus and interaction behavior occurs when focusing a bar. This includes tooltips, and if navigating to a bar where the axis label is hidden, we should display the axis label (once that feature is implemented for non-keyboard nav).
• Additional planning to be done for grouped and trellis bars.
• Additional planning to be done for popover behavior.