I have successfully got a Feed Importer to work, doing a very simple extraction from a Drupal Views RSS feed. Feeling quite pleased with myself, because I have successfully extracted the Title, Description, and Language into a multi-lingual content type built for the purpose.
Now I would like to extract the URL from the feed as well, but I am perplexed as to where to put it. When I look at the dropdown list "Select a target", I can see a series of Drupal targets such as GUID, URL, etc. But what do these actually refer to in Drupal? This is not clear to me at all. I can see when a field that I have added to the content type appears in the list, but what about the default targets (GUID and URL in particular)?
Also, it is not clear to me what makes a target field get the "Used as unique" option