A zip whose members are all images was called cbz from their names alone,
so a folder of holiday photographs came back as a comic. It is now cbz
only when it carries a ComicInfo.xml or is itself named .cbz or .cbr;
otherwise it is unknown, with a note that it is a zip of N images and
would be a comic book if its name said .cbz. Only the archive's directory
is read, so members are still judged by name, and the README says so,
for a wrapped FictionBook too.
{\rtf has to be the whole control word: the byte after it must be the
version digit, a space or the next control word, so {\rtfoo is not RTF.
A FictionBook saved as UTF-16 was unknown. A byte-order mark in either
order now has the front decoded, at most 2048 code units, before the same
walk to the root element.
Four formats a library of ebooks holds and this had no name for, so each
came back as text, as HTML or as unknown.
RTF is its opening group, after any byte-order mark and blank space.
Microsoft Reader is its signature at the front. A FictionBook is XML
whose root element is FictionBook, found by stepping over the
declaration, comments and doctype in the first four kilobytes. That walk
is over bytes rather than text, because a great many FictionBooks are
windows-1251 and would otherwise be called binary; other XML is still
HTML, as before.
A zip whose only real member is one FictionBook is zip-wrapped-fb2, the
same way a zipped PDF is zip-wrapped-pdf: handed to a converter as
FictionBook it is still a zip. A zip whose every real member is a JPEG,
PNG, GIF or WebP is cbz, once directories, ComicInfo.xml and desktop
clutter are passed over. One PDF or one readme among the pages and it is
not a comic. Only the names in the archive's directory are read, as for
every other zip.
The kind vocabulary grows by five: lit, fb2, rtf, cbz and
zip-wrapped-fb2.
funkpower