When passing a description String instead of property name, the Feed plugin renders it in syntax 1.0 instead of using the document's syntax

Currently, in SyndEntryDocumentSource.parseString, the syntax ID to use for rendering is not specified and it defaults to Syntax1.0 because the deprecated method Document.getRenderedContent(String) is used:

return doc.getRenderedContent(mapping.substring(1, mapping.length() - 1));

A simple fix would be:

return doc.getRenderedContent(mapping.substring(1, mapping.length() - 1), doc.getSyntax().toIdString());