An HTML element is keyboard actionable if all the following are true:
- the element is part of sequential focus navigation; and
- the element is visible when focused; and
- it is possible to fire a click event at the element by use of keyboard.
When it is not focused, an actionable element might be visible or not, this is not important as long as the element is visible when it is focused. Similarly, it doesn't matter whether the element can be activated by mouse or other input device as long as it can be activated by keyboard.