Comparison with XML syntax details

##In addition to the extensibility mentioned in the previous article In addition, XML documents are often regarded as the database of documents and the documentation of data. The display-oriented HTML is a little worse in this regard, which results in a significant difference between the two.

1. XMLThere can only be one root element

There can be multiple root elements in HTML, but only one root element is allowed in XML. That is to say, HTML can describe a lot of parallel information, while XML can only describe one, but there are no child elements inside the root element. Quantity limited. For example: HTML can have many parallel table tags as root elements, but XML can have only one root element.

##2.

XMLtag requirements are strict

The start tag must have a matching end tag

In HTML, you can directly use tags such as

without adding an end tag, but in XML, the start tag and end tag must match.

Empty element tags must be closed

Can be used in HTML and other single tags. In XML, empty element tags must be closed. Use a slash (/) to close empty element tags

All tags are case-sensitive

In HTML documents, tags are case-insensitive are the same, but in XML these two are different tags. The capitalization form of the start tag and the end tag must be consistent. .

All tags must be properly nested

All tags in XML must appear in pairs and be nested reasonably.

l All tag attribute values must be enclosed in double quotes or single quotes

In HTML, attribute values can be enclosed in quotes or not. In XML, even numeric characters must be enclosed in double quotes or single quotes, such as .

3. XMLSeparate data and display

Whatever The HTML source code in a web page is mixed with various attributes and tags for auxiliary display, which brings a lot of trouble to the modification of HTML. However, since XML cannot describe the layout and presentation of the page, it is only used to describe data and its structure. Therefore, XML separates data and display. We can design different layouts and presentations for this data, and the data itself does not need to do anything. Revise. The biggest advantage of using XML to represent data is that it is convenient for people and computers to read XML documents and process these data. The way XML represents data is truly independent of the application system, and the data can be reused, and a piece of data can be used in different situations.

It is precisely because of these characteristics of XML that it is very good at processing data, so readers will find that the export of the vocabulary book in Youdao Dictionary is an XML file, and the export of Google Reader It is also an XML file, and the configuration in eclipse is also an XML file... We can think of it this way, In the software development process, as long as it involves the storage and transmission of data, you can consider using XML.

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