Meanwhile, scholars formed the Text Encoding Initiative, which developed consensus guidelines for encoding books and other materials of scholarly interest for a variety of analytic uses as well as reading, and countless literary and other works have been developed using the TEI approach. In the late 1990s, a consortium formed to develop the Open eBook format as a way for authors and publishers to provide a single source-document which many book-reading software and hardware platforms could handle. Several scholars from the TEI were closely involved in the early development of Open eBook. Focused on portability, Open eBook as defined required subsets of XHTML and CSS; a set of multimedia formats (others could be used, but there must also be a fallback in one of the required formats), and an XML schema for a “manifest”, to list the components of a given e-book, identify a table of contents, cover art, and so on. This format led to the open format EPUB. Google Books has converted many public domain works to this open format.
As e-book formats emerged and proliferated, some garnered support from major software companies, such as Adobe with its PDF format that was introduced in 1993. Unlike most other formats, PDF documents are generally tied to a particular dimension and layout, rather than adjusting dynamically to the current page, window, or other size. Different e-reader devices followed different formats, most of them accepting books in only one or a few formats, thereby fragmenting the e-book market even more. Due to the exclusiveness and limited readerships of e-books, the fractured market of independent publishers and specialty authors lacked consensus regarding a standard for packaging and selling e-books.