file explanation

cbz/cbarchives.txt

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+Comic Book Archives (CB7, CBR, CBZ)
+
+A Comic Book Archive is just an archive with a bunch of sequentially-named
+images in it which collate ASCIIbetically to the order in which they should be
+read. Each image corresponds to a page presented by a comic book reader and a
+Comic Book Archive represents a digital comic book.
+
+No guarantees can be made regarding image format, image names (though you can
+expect them to match [:digit:]*\..*; that is, a bunch of numbers followed by a
+file extension), archive attributes (compression or metadata), or what is in
+archives besides the images. In fact, when a comic book only has one image, the
+most common type of file in a comic book archive may not be an image at all.
+
+The extension corresponds to what type of archive is being used. I haven't seen
+an extension that hasn't fit within DOS 8.3, which makes sense as amateur
+skiddies and repackers mostly use Windows.
+
+<http://justsolve.archiveteam.org/wiki/Comic_Book_Archive>
+<https://en.wikipedia.org/wiki/Comic_book_archive>
+
+Here's a table of Comic Book Archive types. I can't imagine this list is
+comprehensive but I can't find more on-line.
+ ____________________  
+| Ext | Archive used |
+|-----|--------------|
+| CB7 | 7-Zip        |
+| CBA | ACE          |
+| CBR | RAR          |
+| CBT | tar(1)       |
+| CBZ | PKZip        |
+'-----'--------------'
+
+I normalize the files I get to the following settings:
+
+ARCHIVE: PKzip. DEFLATE algorithm. No other configuration.
+CONTENTS: ONLY images. Whatever encoding in which I found them.
+	Sequential naming starting from one, with leading zeroes to ensure file
+	names are all the same length.
+
+<https://en.wikipedia.org/wiki/7-Zip>
+7-Zip is free and open source. There are a number of implementations and you
+can easily extract 7-Zip archives on all modern systems.
+
+<https://en.wikipedia.org/wiki/ACE_(compressed_file_format)>
+ACE is a proprietary archive format owned by e-merge GmbH. Nobody uses this.
+There is a free software extractor written in Python available from
+<https://pypi.org/project/acefile> and free software Python implementations
+available for most popular systems.
+
+<https://en.wikipedia.org/wiki/RAR_(file_format)>
+RAR is a proprietary archive format owned by win.rar GmbH. It and CBR are both
+unfortunately pretty common because RAR is popularly considered better at
+compression than PKZip. The reference implementation has a license that is a
+little more permissive than a contract with the devil and support for later
+versions is spotty in free software. I've found it's best to bite the bullet,
+use the reference unrar(1) utility, convert my CBRs to CBZs, and hope I never
+need to use it again.
+
+<https://en.wikipedia.org/wiki/Tar_(computing)>
+TAR (tape archive) is an archive format released in its first incarnation in
+1979. It doesn't do any compression and it's easy to extract files even by hand
+with a hex editor if you can read the binary structure (which is thoroughly
+documented). Tar extractors are ubiquitous, excellent, and built into every
+modern operating system (this notably does not include Windows because
+Microsoft sucks). Later varieties of tar (such as ustar) are standardized (in
+IEEE 1003.1-2017) and files in this format will likely be readable for a very
+long time.
+
+<https://en.wikipedia.org/wiki/ZIP_(file_format)>
+PKZip is free, open source, and like tar's later varieties, standardized (in
+ISO/IEC 21320-1.2015). Archivers and unarchivers are ubiquitous and available
+for all modern operating systems. The format is officially called ZIP but I
+call it PKZip after its original implementation (PKZIP, by Phil Katz) and to
+differentiate it from other "zip" names such as bzip, gzip, and xzip (which are
+all compression algorithms).