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

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

		const sameContent = newContent.content === entry.content;
		const sameMetadata = (equals(newContent.metadata, entry.metadata));
		if (!sameContent || !sameMetadata || !entry.visible) {
			this._sendMessageToWebview({
				type: 'showMarkupCell',
				id: newContent.cellId,
				handle: newContent.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 : newContent.content,
				top: newContent.offset,
				metadata: sameMetadata ? undefined : newContent.metadata
			});
		}
		entry.metadata = newContent.metadata;
		entry.content = newContent.content;
		entry.offset = newContent.offset;
		entry.visible = true;
	}