The page is designed to provide an algorithm to coalesce accessible mutation events like show, hide and reorder events from the same subtree. All accessible mutation events are result of DOM or visibility changes. Events coalescing is used to not spam AT by huge amount of accessible events.
- More older show event target can't be contained by recent show event target. So that if the node was shown then its parent must be visible and therefore we can't get show event for it. Actually this rule is broken if newer event is caused by layout changes.
- More older hide event target can't contain recent hide event target.