EPUB files are publically available e-book standard file types established by IDPF (the International Digital Publishing Forum). They uses various XML and HTML languages. Current criticisms being addressed include the difficulty of utilizing this file type for documents that are exact format dependent, the lack of equation support (without using bitmap images), the lack in detail for linking, and no ability to annotate. These files work similarly to ZIP files. EPUB files are used for most e-readers including the Nook, Kindle, and anything that runs the Kindle market. The intended purpose of the creation of EPUB files is for single use and the sales of text (ie: ebooks). Developed in 2007, this standard file extension uses reflowable content methods, meaning it can easily fit different dimensions of devices for display, similar to the way html text on webpages alters based on zoom and resolution. It can have fixed dimensions for when the intention is for the file to only be viewed in a specific format. EPUB files can include inline raster or vector images and contain DRM support. The most recent versions have four specifications. Publications defines semantics and conformation requirements within the document. Content Documents defines the XHTML, SVG, and CSS usage. Open Container Format defines the file format and processing for capturing resources into a zip container in EPUB.