src/vs/editor/contrib/peekView/browser/peekView.ts/PeekViewWidget/setTitle
class PeekViewWidget:	setTitle(primaryHeading: string, secondaryHeading?: string): void {
		if (this._primaryHeading && this._secondaryHeading) {
			this._primaryHeading.innerText = primaryHeading;
			this._primaryHeading.setAttribute('title', primaryHeading);
			if (secondaryHeading) {
				this._secondaryHeading.innerText = secondaryHeading;
			} else {
				dom.clearNode(this._secondaryHeading);
			}
		}
	}