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.
The .oeb file extension was created for use in accordance with the Open eBook Standard which was overseen by the Independent Digital Publishing Forum (IDPF). This is now a legacy format, having been superseded by the epub file type.
Based on XML, the oeb file defines how multiple sources should be ordered and arranged into a single electronic delivery for the user to consume. This means that there Is one file to be transferred between the vendor and customer rather than multiple files. The file type permits the use of DRM protection. The format was designed to be open and easily used by any online bookstore.