-// Download URLs
-//
-// The following "same origin" URL patterns are supported for public
-// collections (i.e., collections which can be served by keep-web
-// without making use of any credentials supplied by the client). See
-// "Same-origin URLs" below.
-//
-// http://dl.example.com/c=uuid_or_pdh/path/file.txt
-// http://dl.example.com/c=uuid_or_pdh/t=TOKEN/path/file.txt
-//
-// The following "multiple origin" URL patterns are supported for all
-// collections:
-//
-// http://uuid_or_pdh--dl.example.com/path/file.txt
-// http://uuid_or_pdh--dl.example.com/t=TOKEN/path/file.txt
-//
-// In the "multiple origin" form, the string "--" can be replaced with
-// "." with identical results (assuming the upstream proxy is
-// configured accordingly). These two are equivalent:
-//
-// http://uuid_or_pdh--dl.example.com/path/file.txt
-// http://uuid_or_pdh.dl.example.com/path/file.txt
-//
-// The first form minimizes the cost and effort of deploying a
-// wildcard TLS certificate for *.dl.example.com. The second form is
-// likely to be easier to configure, and more efficient to run, on an
-// upstream proxy.
-//
-// In all of the above forms, the "dl.example.com" part can be
-// anything at all: keep-web ignores everything after the first "." or
-// "--".
-//
-// In all of the above forms, the "uuid_or_pdh" part can be either a
-// collection UUID or a portable data hash with the "+" character
-// replaced by "-".
-//
-// In all of the above forms, a top level directory called "_" is
-// skipped. In cases where the "path/file.txt" part might start with
-// "t=" or "c=" or "_/", links should be constructed with a leading
-// "_/" to ensure the top level directory is not interpreted as a
-// token or collection ID.
-//
-// Assuming there is a collection with UUID
-// zzzzz-4zz18-znfnqtbbv4spc3w and portable data hash
-// 1f4b0bc7583c2a7f9102c395f4ffc5e3+45, the following URLs are
-// interchangeable:
-//
-// http://zzzzz-4zz18-znfnqtbbv4spc3w.dl.example.com/foo
-// http://zzzzz-4zz18-znfnqtbbv4spc3w.dl.example.com/_/foo
-// http://zzzzz-4zz18-znfnqtbbv4spc3w--dl.example.com/_/foo
-// http://1f4b0bc7583c2a7f9102c395f4ffc5e3-45--foo.example.com/foo
-// http://1f4b0bc7583c2a7f9102c395f4ffc5e3-45--.invalid/foo
-//
-// An additional form is supported specifically to make it more
-// convenient to maintain support for existing Workbench download
-// links:
-//
-// http://dl.example.com/collections/download/uuid_or_pdh/TOKEN/path/file.txt