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CSS23-fxl_requirements.md

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Fixed-layouts’ Reading Systems Requirements

[Implementers’ doc] [Authors’ doc]

Source: EPUB Content Documents 3.2

There’s a few criteria Reading Systems must meet in order to be conformant:

  • it should allocate the full content display area (i.e. as much of the available Viewport area as possible) for the document;
  • it must use the dimensions expressed in the viewport meta tag to render XHTML Content Documents;
  • it must use the dimensions expressed in the viewbox, and/or x, y, width and height attributes in SVG to render SVG Content Documents.

Styling

You should not inject additional content such as borders, margins, headers or footers into the viewport or the appplication area surrounding the viewport.

Scaling

XHTML (viewport meta)

When the aspect ratio does not match the aspect ratio of the Reading System, you may position the containing block inside the area to accommodate the user interface (letter-boxing).

Content positioned outside the containing block will not be visible.

SVG

SVG is a little bit more complex as there are different options to take into account.

Viewbox attribute

If the SVG only has a viewbox attribute, the coordinate system it defines is mapped to the viewport, keeping the aspect ratio.

Sizing and positioning attributes

If the pixel values defined by x, y, height and width exceed the viewport’s pixel values, the graphic must not be rescaled (it must be clipped on the viewport boundaries).

Both

The coordinate system defined by the viewbox is mapped to the viewport, keeping the aspect ratio.

Notes

The rendition:spread portrait and rendition:viewport are deprecated in EPUB 3.2.

Consequently, the rendition:spread-portrait spine override is deprecated as well.