+{ $notes "Use this to download the file every time." }
+{ $errors "Throws an error if the HTTP request fails." } ;
+
+HELP: download-once-to
+{ $values { "url" { $or url string } } { "file" "a pathname string" } { "path" "a pathname string" } }
+{ $description "If the file exists on disk, returns that pathname without downloading anything. Otherwise, downloads the contents of the URL to a file with the given pathname and returns the pathname." }
+{ $notes "Use this if the contents of the URL are not expected to change." }