CSS的术语定义很重要，还是一个个翻译出来。

3、1定义

StyleSheet ---- 描述文档显示的语句的集合。

Valid StyleSheet-----不用翻译.

Source Document----

Document Language -- html,xml等

Element-----

Replaced Element -----html中，img，input，textarea，select，object就是这类元素。An element for which the CSS formatter knows only the intrinsic dimensions。

Intrinsic dimensions----内在尺度，元素本身定义的宽和高。The width and height as defined by the element itself, not imposed by the surroundings. In CSS2 it is assumed that all replaced elements -- and only replaced elements -- come with intrinsic dimensions.

Attribute---------属性,元素关联的属性，由名称和值构成。

A value associated with an element, consisting of a name, and an associated (textual) value.

Content------内容，没有content的元素称为empty元素。这里的content指的可以是文本，也可以是子元素。如果没有文本或者子元素，则该元素是empty元素。

The content associated with an element in the source document; not all elements have content in which case they are called empty. The content of an element may include text, and it may include a number of sub-elements, in which case the element is called the parent of those sub-elements.

Rendered content-----显示的内容，不一定是本身的内容，可以是alt属性中指定的内容

The content of an element after the rendering that applies to it according to the relevant style sheets has been applied. The rendered content of a replaced element comes from outside the source document. Rendered content may also be alternate text for an element (e.g., the value of the HTML "alt" attribute), and may include items inserted implicitly or explicitly by the style sheet, such as bullets, numbering, etc.

Document tree-----元素构成树，那么content是什么关系呢？

The tree of elements encoded in the source document. Each element in this tree has exactly one parent, with the exception of the root element, which has none.

Child

An element A is called the child of element B if an only if B is the parent of A.

Descendant

An element A is called a descendant of an element B, if either (1) A is a child of B, or (2) A is the child of some element C that is a descendant of B.

Ancestor

An element A is called an ancestor of an element B, if and only if B is a descendant of A.

Sibling

An element A is called a sibling of an element B, if and only if B and A share the same parent element. Element A is a preceding sibling if it comes before B in the document tree. Element B is a following sibling if it comes after B in the document tree.

Preceding element

An element A is called a preceding element of an element B, if and only if (1) A is an ancestor of B or (2) A is a preceding sibling of B.

Following element

An element A is called a following element of an element B, if and only if B is a preceding element of A.

Author-----写文档的人

An author is a person who writes documents and associated style sheets. An authoring tool generates documents and associated style sheets.

User-----看文档的人

A user is a person who interacts with a user agent to view, hear, or otherwise use a document and its associated style sheet. The user may provide a personal style sheet that encodes personal preferences.

User agent (UA)

A user agent is any program that interprets a document written in the document language and applies associated style sheets according to the terms of this specification. A user agent may display a document, read it aloud, cause it to be printed, convert it to another format, etc.

Here is an example of a source document encoded in HTML:

This results in the following tree:

According to the definition of HTML, HEAD elements will be inferred during parsing and become part of the document tree even if the HEAD tags are not in the document source. Similarly, the parser knows where the P and LIs end, even though there are no </P> and </LI> tags in the source.

3.2 Conformance

3.3 Error conditions

3.4 The text/css content type

css的标准类型是 text/css