name of stream? stream-name indexer?

If the specified stream is attached to a file or referent, or is input to the SGML or XML parser, the name of operator will return the name of the file or referent or markup parser. It is an error to invoke the name of operator on a stream that is not attached to a file, a referent or a built-in markup parser.

The herald stream is optional.

It is an error to use the name of test if the stream does not have a name. When in doubt, the test should be preceded by a has name test.