src/vs/editor/browser/viewParts/rulers/rulers.ts/Rulers/constructor
class Rulers:	constructor(context: ViewContext) {
		super(context);
		this.domNode = createFastDomNode<HTMLElement>(document.createElement('div'));
		this.domNode.setAttribute('role', 'presentation');
		this.domNode.setAttribute('aria-hidden', 'true');
		this.domNode.setClassName('view-rulers');
		this._renderedRulers = [];
		const options = this._context.configuration.options;
		this._rulers = options.get(EditorOption.rulers);
		this._typicalHalfwidthCharacterWidth = options.get(EditorOption.fontInfo).typicalHalfwidthCharacterWidth;
	}