Explanation

Code 13 is used to indicate that the logical reading order of a publication is preserved.

In EPUB, the logical reading order is expressed both through the spine element, the' ordering of content documents, and through the markup of each content document. For audio books, the logical reading order is defined by the playlist of tracks.

The logical reading order of the publication must be clearly delineated in the markup. Footnotes, tables, images, sidebars and all similar secondary content must be marked up so that it can be navigated easily.

Examples

Example 1 — Logical reading order 
<ProductFormFeature>
   <ProductFormFeatureType>09</ProductFormFeatureType>
   <ProductFormFeatureValue>13</ProductFormFeatureValue>
</ProductFormFeature>

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