This class represents an instance of a hyperlink which, when activated, causes a bloom book to be downloaded and opened. Such a link looks like bloom://localhost/order?orderFile={path}, where path is appropriate urlencoded. Optionally, it may be followed by &title={title}, where title is the book title (urlencoded). To allow Bloom to be automatically started when such a link is activated requires some registry entries: The key HKEY_CLASSES_ROOT\bloom\shell\open\command must contain as its default value a string which is the path to Bloom.exe in quotes, followed by " %1". For example, "C:\palaso\bloom-desktop\Output\Debug\Bloom.exe" "%1" In addition, the HKEY_CLASSES_ROOT\bloom key must have a default value of "URL:BLOOM Protocol" and another string value called "URL Protocol" (no value). (Don't ask me why...Alistair may know.) One way to set these up on a developer machine is to edit the file bloom link.reg in the project root directory so that it contains the correct path to your exe, then double-click it. When a properly-formed link is followed, a new instance of Bloom is started up and passed the URL as its one command-line argument. This is recognized and handled in Program.Main(). Todo: Make installer set up the registry entries. Todo Linux: probably something quite different needs to be done to make Bloom the handler for bloom:// URLs.