> be kind to the server and only download the file if it's updated
I wonder if their webserver supports the If-modified-since http header
I wonder if their webserver supports the If-modified-since http header
tl;dr: the server doesn't support that header, but since the response does include a Last-Modified header, curl helpfully aborts the transfer if the Last-Modified date is the same as the mtime of the previously downloaded file.