The FictionBook 2.0 file format was developed in Russia and gained popularity there. Whereas other eBook formats contain multiple XML files an FB2 file contains just one. The format is DRM free and is open source. As the name suggests, FB2 files often contain fiction eBooks, however this is not a technical restriction. The format was designed to enable the file to be converted to other file types relatively easily.
The FB2 file contains a tagged structure that allows software applications to interpret and render the content accordingly. This means that elements such as quotations and subtitles can be defined, in addition to formatting such as bold, italic or underline. Typically, an FB2 file contains the Stylesheet, Description and Body. All text to be displayed is contained within the Body section which uses a nested structure to allow subsections and paragraphs to be defined.
AZW3 - Kindle Format 8 (KF8) is Amazon's newer version of AZW. It supports HTML5 and CSS3 which were not supported through the standard AZW format. It has a number of other formatting options and is used by Amazon for all new Amazon eBooks. It is supported by fourth-generation Kindle devices running firmware version 4.1.0 or later and the Kindle Fire device.
KF8 (also called AZW3) is essentially a compiled ePub that has utlises a Palm database and Amazon's DRM scheme. It targets ePub 3 version support but existing ePub can also be used. The internal format has been decoded using mobi_unpack. The basic format remains as a PDB file similar in structure to a MOBI. More oftent than not a KF8 file will contain both a MOBI file at the beginning and the newer KF8 version of ePub later.
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