src/vs/editor/browser/view/domLineBreaksComputer.ts/readClientRect
function readClientRect(range: Range, spans: HTMLSpanElement[], startOffset: number, endOffset: number): DOMRectList {
	range.setStart(spans[(startOffset / Constants.SPAN_MODULO_LIMIT) | 0].firstChild!, startOffset % Constants.SPAN_MODULO_LIMIT);
	range.setEnd(spans[(endOffset / Constants.SPAN_MODULO_LIMIT) | 0].firstChild!, endOffset % Constants.SPAN_MODULO_LIMIT);
	return range.getClientRects();
}