The IDPF is now working on a new version of the EPUB specification, this version 3.1 represents in our opinion a major step forwared.
A second editor's draft was published few days ago.
The latest version of the standard can be seen here.
The original intention was for this version to remove many elements that are not used, change the internal structure of documents etc. however due to community pressure, not all changes where integrated.
However this is still a major step forwared.
The main changes are in the structure of the standard format. The previous versions where more a collection of documents that made it hard to study the standard and understand it's strucutre.
We hope that this new organization will make it easier to understand the standard.
Now instead of being a collection of documents, there is one main document and sub documents that represents sub standards such as the dictionaries standard etc.
Other main changes include removing unneccessary parts of the standard, either because they are obsolete or rarely used by publishers and not supported by reading systems.
The new standard removed the NCX document, It will still be legal to include it, however it will issue a warning.
The guide element that was part of EPUB 2 is now finnaly removed.
Metadata section is now revised, the old meta element used by EPUB2 is removed. The original intention was to remove many other elements.
The major change is inclusion of external metadata that is stored on an external server.
Reading or cataloging systems will be required to fetch an external metadata file that can be in other formats such as MARCXML, MODS, ONIX etc.
Since ONIX is very common as a format for communicating books metadata between publishers and distributors, we think this is a major step forwared.
This does not mean that internal metadata are obsolote, it only serves as a method to help users get the recent version of metadata without the need to have a new version of the EPUB document.
The internal metadata, now includes only minimal set of metadata that is required for reading systems, such as book identifier, title, creator etc.
This set of metadata should be used if for any reason the external resource is not reachable (internet connection, etc.)
The EPUB CFI (Common Fragment Identifier) was removed, it is now not required that reading systems support it, however most reading systems make internal use of a version of CFI to mark part of a document.
I guess it sounds that this version only means obsoleting and removing parts, but no. It also includes additions to the core metadata, a reading system is now required to support more fonts types including WOFF 2.0 and TTF (that is anyway supported by most reading systems but was not part of the core metadata.) the original intention was to add support for other graphic formats and even 3D graphic formats. This was not included since these standards are not mature enough yet.
We hope that the standard will be finalized in the next few month. The intention is to have a final document by October 2016.
Helicon Books has already revised it's production procedures to conform to EPUB 3.1. The Helicon Books reader already conforms to most of it and we are examining what we need to do to fully support the standard.