Only for RSS, you can map an XML property from the feed to the indexing item, such as a custom Author or a Date Published, eg: "Author" with "dc:creator" when XML contains an "<dc:creator>MyName</dc:creator>" property. Note that if the XML contains multiple identical properties, they will be appended with a comma delimiter. For the rest of the URL types (simple page or a sitemap) these properties will be ignored.