In today’s web, various and very different spiders can crawl your website.
Each different spider can look for different meta tags.
As the error message says, the wildcard in question is a 'strict' one, meaning the elements it matches must be declared in the schema.
There may be a way to tell the validator to consult the schema document for the image namespace, but I could not see any obvious one.
This validator checks the markup validity of Web documents in HTML, XHTML, SMIL, Math ML, etc.
If not, the validator will provide you with detailed information about the kinds of errors found and where they are located.Our xml sitemap validator will inform you straight away if there are any problems with your sitemaps allowing you to make changes prior to submitting it to Google.Please note that we would recommend you inform Google of your sitemaps via the Google Search Console.Let’s take a look at how Google, Google’s AMP feature, Bing/Yahoo, Facebook, Twitter, and Pinterest look at your website’s structure and metadata.
Some data can be obtained from the context of the page.
All you really have to do to use the tool is specify a Sitemap file.