Can I see which classes will show up in a table before going through the effort to add it into my webpage?

Yes, you should always check the validity of your code first by previewing the url section of your code in a browser. To view the table results in a browser (outside your website), replace the OpeningsJS part of the code with OpeningsDirect and paste the entire url (starting with https) into a browser window. For an example, see the video for filtering.