An environment in which UAs present documents to users. A tab or window in a Web browser typically contains a browsing context, as does an iframe, or frame elements in a frameset.
Performing a case-insensitive match between two strings means comparing the strings exactly, codepoint for codepoint, except that the characters in the range A-Z and the corresponding characters in the range a-z are considered to also match.
Some embedded content elements can have fallback content: content that is to be used when the embedded content cannot be used (for example, when it is of an unsupported format).
Flow content consists of flow elements intermixed with normal character data.
HTML user agents; that is, applications (such as Web browsers) which consume HTML content.
HTML authors (that is, people) and applications (such as editors and content management systems) that produce HTML content.
A newline may be represented as any of the following:
U+000D CARRIAGE RETURN (CR) character
U+000A LINE FEED (LF) character
U+000D CARRIAGE RETURN (CR) followed by a U+000A LINE FEED (LF) character
Phrasing content consists of phrasing elements intermixed with normal character data.
A space character is any of the following:
U+0009 CHARACTER TABULATION (tab)
U+000A LINE FEED (LF)
U+000C FORM FEED (FF)
U+000D CARRIAGE RETURN (CR)
If the content model of a particular element is described as transparent, it means:
When an element is a child of a parent element whose content model is allowed to contain flow elements, then the content of the element may also contain flow elements.
When an element is a child of a parent element whose content model restricts its child elements to only being phrasing elements, then any child elements of the element are also restricted to only being phrasing elements.
W3C HTML: The Markup Language