In order to be able to use mupdf as a document reader, one of the essential
features is to be able to automatically fit the document zooming level to the
window size (and adapt the window level if the window is resized).
'W' would be a good shortcut for it. Right now, this shortcut is used to the
opposite action (fit the window size to the actual document width). I wonder
whether this is really useful (I really don't know what it could be useful for).
And it might be counterintuitive for users, since xpdf defines this shortcut to
fit to document width to window width.
Just in case it helps,
*** This bug has been marked as a duplicate of bug 691330 ***