intertwingly

Rafe Colburn: I didn’t know until just now that you don’t need to include the closing ?> in PHP files that consist entirely of code. The Drupal coding standards explain why you probably want to leave it out:

Note that the final ?> should be omitted from all code files–modules, includes, etc. The closing delimiter is optional, and removing it helps prevent unwanted white space at the end of files which can cause problems elsewhere in the system.

News to me too.  This may also be the cause of a rather common feed error.  I’ve added the recommendation to the front of the solution section in the hopes that it helps somebody.