src/vs/editor/browser/viewParts/viewZones/viewZones.ts/ViewZones/constructor
class ViewZones:	constructor(context: ViewContext) {
		super(context);
		const options = this._context.configuration.options;
		const layoutInfo = options.get(EditorOption.layoutInfo);

		this._lineHeight = options.get(EditorOption.lineHeight);
		this._contentWidth = layoutInfo.contentWidth;
		this._contentLeft = layoutInfo.contentLeft;

		this.domNode = createFastDomNode(document.createElement('div'));
		this.domNode.setClassName('view-zones');
		this.domNode.setPosition('absolute');
		this.domNode.setAttribute('role', 'presentation');
		this.domNode.setAttribute('aria-hidden', 'true');

		this.marginDomNode = createFastDomNode(document.createElement('div'));
		this.marginDomNode.setClassName('margin-view-zones');
		this.marginDomNode.setPosition('absolute');
		this.marginDomNode.setAttribute('role', 'presentation');
		this.marginDomNode.setAttribute('aria-hidden', 'true');

		this._zones = {};
	}