HTML5 の 2010 年 3 月 4 日付 W3C 草案 では、aside 要素は以下のように定義されています: The aside element represents a section of a page that consists of content that is tangentially related to the content around the aside element, and which could be considered separate from that content. Such sections are often represented as sidebars in printed typography. The element can be used for typographical effects like pull quotes o