src/vs/workbench/contrib/debug/browser/watchExpressionsView.ts/WatchExpressionsView/onMouseDblClick
class WatchExpressionsView:	private onMouseDblClick(e: ITreeMouseEvent<IExpression>): void {
		if ((e.browserEvent.target as HTMLElement).className.indexOf('twistie') >= 0) {
			// Ignore double click events on twistie
			return;
		}

		const element = e.element;
		// double click on primitive value: open input box to be able to select and copy value.
		if (element instanceof Expression && element !== this.debugService.getViewModel().getSelectedExpression()) {
			this.debugService.getViewModel().setSelectedExpression(element);
		} else if (!element) {
			// Double click in watch panel triggers to add a new watch expression
			this.debugService.addWatchExpression();
		}
	}