src/vs/editor/browser/viewParts/lines/viewLine.ts/RenderedViewLine/getColumnOfNodeOffset
class RenderedViewLine:	public getColumnOfNodeOffset(lineNumber: number, spanNode: HTMLElement, offset: number): number {
		const spanNodeTextContentLength = spanNode.textContent!.length;

		let spanIndex = -1;
		while (spanNode) {
			spanNode = <HTMLElement>spanNode.previousSibling;
			spanIndex++;
		}

		return this._characterMapping.getColumn(new DomPosition(spanIndex, offset), spanNodeTextContentLength);
	}