The non-listable tags are similar to properties on each object. You can read / set their values once you have retrieved the object. You cannot list on them.  Thanks, Aashish
Can someone give me an example of why you would have a Metadata tag that is not listable?  For example, if I create listable tags of files uploaded by year (let's say 2010, 2011,2012) I can list these tags by using getListableTags. What about the unlistable ones? I've tried the equivalent of getListableTags('privatetag'); and it's gives an ESUException when I use the ESU PHP Framework.
Why Have MetadataTags that are not listable?