ePub 3 rules
- Publication title: Checks that the EPUB’s title is defined in the Package Document.
- Accessibility metadata: Checks that schema.org accessibility metadata is defined in the Package Document.
- Page break source: When content has page breaks, checks that the print source is identified in metadata with dc:source.
- Also checks HTML5 accessibility rules.
 The tool
The easiest way to use Ace is a command line.
Ace by DAISY, an Accessibility Checker for EPUB Usage: ace [options] <input> Options: -h, --help output usage information -v, --version output the version number -o, --outdir <path> save final reports to the specified directory -t, --tempdir <path> specify a custom directory to store the temporary reports -f, --force override any existing output file or directory --subdir output reports to a sub-directory named after the input EPUB -V, --verbose display verbose output -s, --silent do not display any output Example: $ ace -o out ~/Documents/book.epub
 Accessibility standards
This Accessibility specification from idpf does not target a single version of EPUB. It is designed to be applicable to EPUB Publications that conform to any version or profile, including future versions of the standard. There are three levels of compliance.
- The lowest level is called Discovery. It includes metadata in the package that defines some details about how accessible this particular ePub is and any hazards that might be in the document.
- The second level is called Accessible. This level requires level one plus some actual accessible features must be present in the eBook.
- The highest level is called Optimized. This level requires both of the previous levels and provides a general set of guidelines for making content broadly accessible, however conformant content is not always optimal for specific user groups. Conversely, content optimized for a specific need or reading modality is often not conformant because it is not designed for a broad audience.