EuiComboBox

[cjcenizal]

Prototype: #52

Taken from elastic/kibana#12543:

Extracted from elastic/kibana#12325.

We need to implement ARIA accessibility for this component:

• Alt + Down: If the input has focus, open the dropdown.
• Alt + Up: Close the dropdown and focus the input.
• Up/Down: Move focus to the previous/next option.
• Page Up/Down: Move focus to the previous/next page's option.
• Escape: Close the dropdown and focus the input.
• Enter: If an option is focused, select it, close the dropdown, and focus the input.
• (Any character): If an option is focused, move focus to the option that begins with that character.

References to the draft spec:

• https://www.w3.org/TR/wai-aria-1.1/#combobox
• https://www.w3.org/TR/wai-aria-practices-1.1/#combobox
• https://rawgit.com/w3c/aria-practices/master/aria-practices-DeletedSectionsArchive.html#autocomplete
• https://rawgit.com/w3c/aria-practices/master/aria-practices-DeletedSectionsArchive.html#combobox

References to similar components:

• http://jedwatson.github.io/react-select/
• https://github.com/reactjs/react-autocomplete

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Per comment by @chrisronline:

One accessibility problem we need to avoid is ensuring that, assuming multiple selections are enabled, the user can reselect previously selected items and remove them and be notified of which are removed. With ui-select, they can just backspace to remove them but they can't choose which ones to remove or aren't even told which ones were removed. Maybe have the tab button go through the selected options before exiting out of the control?

[snide]

Closing this now that it's in. We have follow up issues for additional feature work on this component.