xml 文档树

XML documents form a tree structure that starts at "the root" and branches to "the leaves".
XML 文档树起始于“根元素”，并以此为基础扩展文档的分支结构。

An Example XML Document
下面举一个XML文档案例

XML documents use a self-describing and simple syntax:
XML 文档使用一种相对简单的自述性语法：

The first line is the XML declaration. It defines the XML version (1.0) and the encoding used (ISO-8859-1 = Latin-1/West European character set).
代码的第一行对XML文档做出了声明。它定义了XML版本号（1.0）以及文档所使用的字符编码（ISO-8859-1：拉丁文/西欧字符集）。

The next line describes the root element of the document (like saying: "this document is a note"):
接下来的一行定义了文档的根元素（指明该文档是一份便条）：

<note>

The next 4 lines describe 4 child elements of the root (to, from, heading, and body):
再接下去的4行定义了根元素的4个子元素，分别是“to”、“form”、“heading”和“body”：

And finally the last line defines the end of the root element:
文档的最后一行定义了根元素的结束标签：

</note>

You can assume, from this example, that the XML document contains a note to Tove from Jani.
举个例子来说，你可以假设这份XML文档是Jani递交给Tove的一张便条。

Don't you agree that XML is pretty self-descriptive?
通过上述案例，对于XML是一种完美的自述性语言这点应该毋庸置疑了吧？

XML Documents Form a Tree Structure
XML 树状结构文档

XML documents must contain a root element. This element is "the parent" of all other elements.
XML 文档必须包含一个根元素。这个根元素是其它所有元素的“父元素”。