Sets or gets the SEO markup to be rendered for search engine bots.
Use the seoMarkup property to write HTML content that will be served to Google and other search engines. This is necessary because some bots cannot process the JavaScript content of the custom element.
If you do not add the equivalent HTML of the custom element's implementation using this SEO markup property, only bots that index JavaScript, such as Google, will be able to index the custom element's content/markup for search engine results.
Note: It is the user's responsibility to handle all aspects of SEO for the element, including managing the validity of the SEO markup opposite search engines.