Accessibility metadata in epub content.opf

[jgm]

Discussed in #9365

^{Originally posted by Iacobus1983 January 25, 2024}
In view of EU Accessibility Act, I checked a pandoc-generated epub with DAISY Ace (1.3.2). I get some accessibility warnings.

In order to make the epubs compliant with accessibility requirements, it seems that minor addition to content.opf would be needed:

1. xml:lang attribute should be added to package element, most likely with the same value of dc:language element (see https://kb.daisy.org/publishing/docs/wcag/language-of-page.html)
2. Accessibility meta elements:

• schema:accessMode, schema:accessibilityFeature and schema:accessibilityHazard are mandatory;
• schema:accessModeSufficient and schema:accessibilitySummary are optional.

Full support for metadata mentioned in point 2 would possibly require a user-defined input, e.g. within the metadata yaml file (perhaps similar to 743d1b3 ?)