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Glossary

What is reading order?

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Reading order is the sequence in which text is meant to be read: column by column, with side notes, captions and footnotes placed where they belong. In an EPUB it is set by the spine and the order of elements in each document.

Why it matters when you convert a PDF to EPUB

A PDF stores text in drawing order, which can jump between columns, headers and captions. Recovering the reading order is the hardest part of converting multi-column documents: reading straight across two columns mixes two unrelated sentences on every line.

How EpubCC handles it: the engine cuts each page recursively at its widest gaps (an XY-cut), treating a vertical gap as a column break only when each side has at least two lines, and keeps images in the flow as pseudo-words. A paragraph interrupted by a column or page break is joined to the next part when the sentence continues in lowercase.

Related terms

EPUBCheck messages about this

  • NAV-011 "…" nav must be in reading order; link target "…" is before the previous link’s target in … order.
  • MED_015 Media overlay text references must be in reading order. Text target "…" is before the previous link target in … order.

See how EpubCC keeps columns in order
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FAQ

What is reading order?

Reading order is the sequence in which text is meant to be read: column by column, with side notes, captions and footnotes placed where they belong. In an EPUB it is set by the spine and the order of elements in each document.