Flowing Books: Font Guidelines
When specifying line-height, set the value to a unit-less multiple of the font-size, for example, line-height: 1.2;. Including units, such as em or %, can cause lines of text to overlap if allowed to cascade to an element with a font-size that is larger than the element on which the line-height was declared.
Text Alignment: Clarification
iBooks provides a preference that a user can choose to display the text in a book to full justification. This option overrides any text alignment you specify and justifies all paragraphs in a book. You can preserve your text alignment by using the specified-fonts attribute and set it to true. This attribute preserves the font settings as specified in your CSS stylesheet, as long as the user does not choose a different font when reading the book. See Fonts Overview for more information on fonts and see Defining Book Layout Metadata for information on using specified-fonts.
Pop-Up Footnotes: Clarification
When adding pop-up footnotes in EPUB 3 books, you can use the <aside> element as explained in Pop-up Footnotes or you can use a <div> or <p> element. You can replace the <aside> element with a <div> or <p> element. Use the <aside> element when you want to hide the footnote; use a <div> or <p> element when you want the footnote to appear in the normal reading view. If you use <div> or <p> and a user clicks the footnote link, the content appears in a popup, but the footnote is also visible as part of the text on the page.
Flowing Books: Font Sizing Correction
In previous versions of this guide, it was recommended that when sizing fonts in flowing books, you should use either em or pixel (px) units. However, using pixel units prevents users from adjusting the font size. Font sizes should be defined in em or percentage (%).
Interior Images: Correction
In the following image guideline, the svg:img was changed to svg:image: To ensure proper viewing of images in content, use the HTML img tag instead of wrapping images in svg:image.