There's not much that can be done about this. The HTML box model says that they do indeed overlap, it's just the text flow algorithm that stops them colliding.

The only way to stop them colliding would be:

• Use display:table instead of block, but this would likely cause more unforseen problems. We try not to restyle elements as much as possible.
• Calculate the highlights based on text content. This would be very slow, and potentially ugly.

I think we could notably improve 99% of the cases here by just having some extra handling for Focusable nodes that are outside of normal flow (absolutely positioned or floated, "out-of-flow").

Basically, pre-calculate focusable highlights for out-of-flow nodes (there should not be very many, even https://en.wikipedia.org/wiki/Barack_Obama only has about 60, see test function below), then when displaying any focusable highlights for a node in-flow, mask/subtract the out-of-flow highlights (this might require T190226 first).

A references list colliding with an infobox is the most common case, but this can also happen with e.g. block-template/gallery colliding with e.g. image/mapframe.

Function to determine whether a DOM element is out-of-flow, per the "cheatsheet" at https://www.w3.org/TR/CSS22/visuren.html#dis-pos-flo:

$('.ve-ce-surface *:not(.oo-ui-iconElement-icon)').filter(function isOutOfFlow(i, elem){
	var
		display = $(elem).css('display'),
		position = $(elem).css('position'),
		float = $(elem).css('float');
	if ( display === 'none' ) return false;
	if ( position === 'absolute' || position === 'fixed' ) return true;
	if ( float !== 'none' ) return true;
	return false;
})

Why merge the wrong way?

This task had recent discussion.

A year ago is hardly recent.

In T104540#4067124, @matmarex wrote:

I think we could notably improve 99% of the cases here by just having some extra handling for Focusable nodes that are outside of normal flow (absolutely positioned or floated, "out-of-flow").

FYI doing computed CSS is very slow, so would need to be done on an on-hover basis, not for all templates on the page on load.