Your ePub Is fine

Original Article ↗ Hacker News Discussion ↗

EPUB’s promise as an open ebook standard is running into real‑world compatibility problems, particularly on Kobo devices that rely on Adobe’s aging RMSDK rendering engine. Commenters describe valid EPUBs failing to open because the Adobe stack mishandles basic CSS rules it is supposed to ignore, raising questions about standards that evolve quickly versus embedded devices that rarely update and about tools like epubcheck that validate specs but not actual devices. Many readers work around the issues with Kobo-specific KEPUB formats, alternative software such as KOReader, or more open hardware, while broader frustrations with DRM and closed ecosystems echo past grievances with technologies like Flash.

EPUB, CSS, and Standards Compliance

  • EPUB is essentially zipped HTML/CSS; in theory easy to render and edit, in practice implementations are inconsistent.
  • CSS is designed to be forward compatible: unknown/illegal declarations should be ignored, not cause failures. Several comments state ADE/RMSDK violate even CSS1 rules by treating minor CSS issues as fatal.
  • EPUB 3+ tied itself to “living” browser specs (WHATWG HTML, modern CSS), which move faster than embedded e-readers. This made some older EPUBs technically non‑conforming, so many tools still target EPUB 2 or 3.1.
  • Debate: some argue the spec is over-ambitious for slow-moving devices; others insist implementations should simply follow the spec and ignore unknown CSS.

Kobo, RMSDK, and Kepub

  • Kobo’s Adobe-based RMSDK engine is widely described as outdated and brittle, rejecting otherwise valid EPUBs.
  • Workaround: convert EPUBs to Kobo’s kepub format (e.g., via Calibre plugins or kepubify). This uses a different renderer with better layout, features (e.g., cross-page highlighting), and fewer compatibility issues.
  • Multiple users install KOReader or Plato as alternative renderers; these often handle EPUBs and PDFs better and ignore problematic CSS.
  • Kobo is reportedly rewriting its software (especially in the EU, tied to accessibility rules) and may be moving away from Adobe DRM, but details and trade-offs are unclear.

EPUB vs PDF and Minimalism

  • Some prefer PDF despite its notoriously complex internals because reader behavior is more predictable and legacy-compatible.
  • Others prefer EPUB but advocate using extremely simple HTML/CSS (or even plain text) to maximize compatibility across old and buggy readers.
  • Several readers strip “fancy” styling, embedded fonts, and modern CSS, arguing ebooks rarely need complex layout.

DRM, Ecosystems, and Device Openness

  • ADE-style DRM is seen as fragile and exclusionary: hard to support as a third-party, and a barrier to new reader software.
  • People describe stripping DRM (when possible) to get standard EPUBs; some library users say ADE no longer works on their systems.
  • Comparisons: Kindle praised for reliability but criticized for lock-in and dependence on Amazon services; Kobo, PocketBook, Boox, PineNote, and other Linux/Android-based devices are discussed as more hackable/open, but with stability, UX, or cost trade-offs.

Adobe, Flash, and Broader Sentiment

  • Strong anti-Adobe sentiment: products viewed as DRM-first and poorly maintained (RMSDK, Flash, sometimes PDF tools).
  • Long tangent compares Flash’s creative power and ease of publishing versus its security, performance, and proprietary problems; used as an analogy for Adobe’s handling of EPUB tech.