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                      Features that have a direct effect on the reading system behavior, and whose behavioral details are mostly specified by <a href="https://www.w3.org/TR/epub-rs-33/">EPUB 3.3 Reading Systems</a>. Examples are the list of <a href="https://www.w3.org/TR/epub-33/#sec-core-media-types">supported media types</a>, semantics of some <a href="https://www.w3.org/TR/epub-33/#attrdef-dir">internationalization features</a>, or the <a href="https