?stylesheet=...request parameter proved especially useful to render a single Part file, using a stylesheet that can be globally defined at Book level (with
mapstylesheetscommand). As I blogged the Book file heads towards carrying more and more configuration stuff. So, a
?book-configuration=...request parameter would make sense, in order to reuse Book's configuration, like stylesheet, encoding, hyphenation language and probably more. Because a Book could define Part-specific configuration, those must be taken in account if the Part if one of those included by the Book.