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 .pdb file extension is a database format used for the Palm OS platform. The PalmDOC eBook file type is a version of the PDB format. The proliferation of eBooks has left this format behind due to the lack of support for DRM protection meaning only royalty free text is typically available.
The format supports reflowable content however the format lacks some of the features found in more modern eBook formats, for example only providing a very basic contents table. The format features RLE compression which was crucial because the format was designed for the low storage capacity Palm devices of the 1990s.