Well-Formed XML

最新推荐文章于 2023-05-30 21:00:00 发布

王的盛饭

最新推荐文章于 2023-05-30 21:00:00 发布

阅读量1k

点赞数

分类专栏： java语言文章标签： constraints xml exception tags nested table

java语言专栏收录该内容

7 篇文章

订阅专栏

本文介绍了XML文档的基本规范，包括文档必须具有一致且定义明确的结构、所有属性值需引用、空白字符的重要性、开始标签与结束标签的对应关系等。要使文档有效，除了遵循这些基本规范外，还需符合DTD或XML Schema的约束。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

In this section, we explain the various syntactical rules of XML. Documents that follow these rules are called well-formed, but not necessarily valid, as we'll see. If your document breaks any of these rules, it will be rejected by most, if not all, XML parsers.

Well-Formedness

The minimal requirement for an XML document is that it be well-formed, meaning that it adheres to a small number of syntax rules, which are summarized in Table 3-1 and explained in the following sections. However, a document can abide by all these rules and still be invalid. To be valid, a document must both be well-formed and adhere to the constraints imposed by a DTD or XML Schema.

Table 3.1 XML Syntax Rules (Well-Formedness Constraints)
The document must have a consistent, well-defined structure.
All attribute values must be quoted (single or double quotes).
White space in content, including line breaks, is significant.
All start tags must have corresponding end tags (exception: empty elements).
The root element must contain all others, which must nest properly by start/end tag pairing.
Elements must not overlap; they may be nested, however. (This is also technically true for HTML. Browsers ignore overlapping in HTML, but not in XML.)
Each element except the root element must have exactly one parent element that contains it.
Element and attribute names are case-sensitive: Price and PRICE are different elements.
Keywords such as DOCTYPE and ENTITY must always appear in uppercase; similarly for other DTD keywords such as ELEMENT and ATTLIST.
Tags without content are called empty elements and must end in "/>".