function metaIdentifier (tag) {
  for (const item of ['name', 'property', 'itemprop']) {
    if (tag.hasOwnProperty(item)) return tag[item] + item
  }
  return JSON.stringify(tag)
}
Try to identify a meta tag by name, property or itemprop

Return a complete string if none provided
@param {Object} tag from frontmatter or siteMetaTags
@returns {String}