EPUB3, WCAG, EAA, PDF/UA — terms explained for compliance teams and document publishers
Definitions for standards, regulations, file formats, tools, and document types used in document accessibility and EAA 2026 compliance. Updated July 2026.
Web Content Accessibility Guidelines version 2.1. Published by the W3C in 2018. The international standard for digital content accessibility. Organised into four principles (Perceivable, Operable, Understandable, Robust) and three conformance levels (A, AA, AAA).
WCAG 2.1 Level AA is the compliance target for the EAA, EN 301 549, UK Accessibility Regulations, and most national digital accessibility laws. If a regulation says "accessible", it almost always means WCAG 2.1 AA.
A Success Criterion in WCAG 2.1. Requires that content can be presented without loss of information or functionality, and without requiring scrolling in two dimensions, at a viewport width equivalent to 320 CSS pixels (i.e., at 400% zoom on a 1280px-wide display).
The 400% rule: 400% zoom is the standard level used by many people with low vision to make text readable. WCAG 1.4.10 was added specifically to address this user group — it was not present in WCAG 2.0.
Fixed-layout PDF fails this criterion for any document with multi-column layout, complex formatting, or wide tables. EPUB3 satisfies WCAG 1.4.10 by design — content reflows to the available viewport width at any zoom level.
The compliance level most commonly required by regulation. Includes all Level A and Level AA success criteria — 50 criteria in total across WCAG 2.1.
Referenced by: the EAA (Directive 2019/882), UK Accessibility Regulations 2018, US Section 508, EN 301 549, Irish Accessibility Act, and most EU member state implementations of the Web Accessibility Directive.
European harmonised standard for ICT accessibility. Incorporates WCAG 2.1 AA and extends its requirements to non-web contexts:
• Clause 10: Non-web documents — PDFs, EPUB files, Word documents published on websites
• Clause 11: Non-web software — desktop applications, mobile apps, ebook reading systems
EN 301 549 Clause 10.1.4.10 is the Reflow requirement applied to downloadable documents. It has applied to public sector documents in the EU since 2020.
PDF Universal Accessibility. ISO standard for accessible PDFs. Requires correct tagging structure: headings, reading order, alt text on images, language declarations, tagged tables.
What PDF/UA does not fix: WCAG 1.4.10 Reflow — a criterion that cannot be satisfied by fixed-layout PDF regardless of tagging quality. PDF/UA is necessary but not sufficient for WCAG 2.1 AA compliance.
Tools that produce PDF/UA: Adobe Acrobat Pro with accessibility checker, CommonLook, axesPDF, PAC 2024.
The W3C/DAISY accessibility specification for EPUB ebooks. Published in 2023. Incorporates WCAG 2.1 AA and adds EPUB-specific requirements: EPUB navigation document (table of contents), accessibility metadata in the OPF package file, sufficient reading system compatibility.
The EAA references EPUB Accessibility 1.1 as the standard for e-book publishers. The ACE by DAISY validator tests against this specification.
A file format for ebooks, standardised by the W3C. Built on HTML5, CSS, and SVG. Content is reflowable by default — it adapts to the viewport width, font size, and zoom level set by the reader. EPUB3 can satisfy WCAG 1.4.10 Reflow; fixed-layout PDF cannot.
File extension: .epub
Supported by: Thorium Reader, Apple Books, Kobo devices, Google Play Books, Kindle (via conversion), most modern ebook reading systems.
EPUB3 is the format recommended by the DAISY Consortium for accessible document distribution and is the accessible output format produced by toolkit.bot.
A variant of EPUB3 in which page dimensions are fixed and content does not reflow. Used for children's picture books, graphic novels, and highly designed content. Fixed-layout EPUB has the same WCAG 1.4.10 Reflow problem as PDF — content does not reflow at high zoom.
toolkit.bot produces reflowable EPUB3, not fixed-layout EPUB.
Portable Document Format. Designed for print fidelity — content is fixed to page dimensions. Widely used for official document distribution. PDF/UA (ISO 14289) adds structural accessibility tagging, but the fixed-layout model means PDF cannot satisfy WCAG 1.4.10 Reflow for complex layouts.
When to keep PDF: Regulatory submissions, print-quality archiving, documents requiring digital signatures, forms.
When to add EPUB3: All documents distributed digitally for reading — the EPUB3 serves as the accessible reading version alongside the PDF.
Directive 2019/882 of the European Parliament and of the Council. Requires that specified products and services are accessible under WCAG 2.1 AA. Enforcement active from June 28, 2026.
Covered sectors (document accessibility relevant):
• E-commerce and online retail
• Banking and financial services
• Insurance
• Electronic communications (telecoms)
• Passenger transport (air, rail, ferry, bus/coach)
• E-book publishers and e-reading software
• Audio-visual media services
Enforcement: National market surveillance authorities in each EU member state. Complaint-based — consumer organisations, disabled users, and competitors can file complaints.
See also: How PDF-to-EPUB3 satisfies the EAA →
Enterprises with fewer than 10 employees AND annual turnover or balance sheet total not exceeding €2 million are exempt from the EAA. This matches the definition of micro-enterprise under EU Recommendation 2003/361/EC.
Small enterprises (10–49 employees) are not exempt but may receive proportionality assessments. Medium and large enterprises are fully in scope.
The Public Sector Bodies Accessibility Regulations. Implements the Web Accessibility Directive for the UK. Requires public sector websites and mobile apps to meet WCAG 2.1 AA. Extends to downloadable documents (non-web documents) via EN 301 549 equivalent requirements.
Applies to: central government, local government, NHS, universities, and other public bodies.
Requirement for NHS and social care providers to identify, record, and meet the communication needs of patients and service users. Requires that information is provided in the format a patient needs — including accessible digital formats for patients with visual impairments.
EPUB3 satisfies this standard for digital document distribution.
Accessibility Checker for EPUB by the DAISY Consortium. The reference validator for EPUB Accessibility 1.1 and WCAG 2.1 AA conformance in EPUB3 files. Produces an HTML report with pass/fail results for each WCAG criterion, including WCAG 1.4.10 Reflow.
Used as evidence in EAA compliance documentation.
Install: npm install -g @daisy/ace
Run: ace --outdir ./report ./document.epub
Free tool from the PDF Association for testing PDF/UA and WCAG 2.1 conformance in PDFs. Identifies tagging failures. Does not test WCAG 1.4.10 Reflow — which is by design, since PDF cannot satisfy that criterion.
Free, open-source EPUB3 reading application available for Windows, macOS, and Linux. Fully compatible with screen readers (NVDA, JAWS, VoiceOver). The reference reading system for testing EPUB3 accessibility. Maintained by EDRLab.
The Digital Accessible Information System Consortium. An international group of organisations working on accessible publishing. Developed the ACE validator. Co-authored EPUB Accessibility 1.1 with W3C. The DAISY format predates EPUB3 and focuses on accessible audiobooks and talking books; modern DAISY work focuses on EPUB Accessibility 1.1.
The international web standards body. Publishes WCAG (Web Content Accessibility Guidelines) and co-publishes EPUB Accessibility 1.1 with DAISY. The Accessible Rich Internet Applications (ARIA) specification — used in EPUB3 for landmark roles — is also a W3C standard.
The EU agency responsible for scientific evaluation of medicines. Mandates the format of Patient Information Leaflets (PILs) distributed with medicines. The standard EMA PIL format — typically two columns — is structurally inaccessible under WCAG 1.4.10 as a fixed-layout PDF. EPUB3 conversion produces a compliant accessible reading version.
The document included with licensed medicines, regulated by the EMA and national medicines agencies. Required content is mandated (indications, contraindications, dosing, side effects, storage). The standard PIL format uses a two-column layout that fails WCAG 1.4.10 in PDF form. Accessible PIL distribution requires EPUB3 or equivalent reflowable format.
A pre-contractual disclosure document required by the EU PRIIPs Regulation (1286/2014) for Packaged Retail and Insurance-based Investment Products. Mandated two-page, two-column format. Required to be provided to retail investors before purchase. As a fixed-layout PDF, it fails WCAG 1.4.10. EPUB3 provides the accessible reading version.
A standardised pre-contractual document for non-life insurance products, required by the EU Insurance Distribution Directive (IDD). Fixed-format two-page PDF. Fails WCAG 1.4.10 in PDF form.
Documentation provided with medical devices, regulated under EU MDR (2017/745) and IVDR (2017/746). Where IFUs are distributed digitally, they must satisfy EAA accessibility requirements. Complex IFU layouts (technical diagrams, warning tables, step-by-step instructions) typically fail WCAG 1.4.10 in PDF form.
toolkit.bot converts PDFs to reflowable EPUB3 that satisfies WCAG 1.4.10 Reflow and targets EPUB Accessibility 1.1. No signup required.
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