src/vs/workbench/contrib/notebook/browser/view/renderers/backLayerWebView.ts/BackLayerWebView/showMarkupPreview
class BackLayerWebView:	async showMarkupPreview(initialization: IMarkupCellInitialization) {
		if (this._disposed) {
			return;
		}

		const entry = this.markupPreviewMapping.get(initialization.cellId);
		if (!entry) {
			return this.createMarkupPreview(initialization);
		}

		const sameContent = initialization.content === entry.content;
		if (!sameContent || !entry.visible) {
			this._sendMessageToWebview({
				type: 'showMarkupCell',
				id: initialization.cellId,
				handle: initialization.cellHandle,
				// If the content has not changed, we still want to make sure the
				// preview is visible but don't need to send anything over
				content: sameContent ? undefined : initialization.content,
				top: initialization.offset
			});
		}

		entry.content = initialization.content;
		entry.offset = initialization.offset;
		entry.visible = true;
	}