Files with .fb2 extension are FictionBook 2.0 eBook files that contains the structure of the eBook. It is based on XML format and contains special tags for describing each element of the book. It was developed primarily for fictional writings and literature, but is not limited to these only. The format accommodates all the metadata as well as content in itself and allows flexibility for a number of operations such as automatic processing, indexing, and conversion to other formats. In short, it focuses on describing the structure of the file instead of specifying its appearance. Several applications as well as APIs are available to convert FB2 to several other formats on Windows, MacOS, and Linux.
FB2 File Format
The FictionBook 2.0 file format was developed by Dmitry Gribov of FictionBook in Russia. Unlike other popular Ebook file formats such as EPUB that contain multiple XML files, it is based on a single XML file that contains complete information about the contents. If there are images inside the file such as PNG or JPG, these are converted to Base64 and embedded inside the document. The file format specifications for FB2 contains information for the version 2.0 of the format.