XML syntax structure

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The above is A basicXML, we will use this as an example to explain the structure and syntax of theXMLdocument in detail.

##XML

Declaration (line 1)XML

Documents always begin with aXMLdeclaration, which indicates theXMLversion, document encoding and document independence information.The format is:

Version information[Encoding information][Document independence information]?>，Among them, brackets( The parts in [])represent optional information.

1.Version description:

It should be noted that there are question marks before and after. And there can be spaces between question marks and brackets, otherwise an error will occur. As of the time the author posted the blog, there were two versions ofXML1.0and1.1, the implementation details are different between different versions. When a low-versionXMLprocessor parses a high-versionXMLdocument, it may encounter some unrecognized symbols. or syntax, resulting in incorrect parsing results.XMLis processed by writing theXMLdeclaration at the beginning of theXMLThe processor can judge theXMLspecification that the document complies with based on the declaration. If it encounters an unsupported version, it will no longer parse and process it, and an error message will be given directly.

2.Document encoding declaration

inXMLdeclaration You can also add document encoding information. The default isUTF-8. If you want to use Chinese, you can addencoding=# to the statement. ##”gb2312” What needs to be noted is the encoding ofXMLandencodingThe encoding of the attribute must correspond, otherwise the following error will be reported "Switching from the current encoding to the specified encoding is not supported. Processing resources...".

For example: Use Notepad to saveXMLasANSIencodingThe attribute ofshould begb2312; when saved with Notepad asUTF-8encoding Theattribute should beUTF-8, and the same applies to other encodings.

3.Independent document declaration

If our document does not depend on external documents, inXMLIn the declaration, you can declare that this document is independent bystandalone="yes" document. If the document depends on an external document, it can be declared bystandalone="no". The completeXMLdeclaration looks like this:

Document type declaration (line 2)

Through the introduction in the previous article, we know that we can useDTD(Document Type Definition, document type definition) To standardizeXMLdocuments.XMLInherits theDTDmechanism for defining syntax rules fromSGML,ButDTDitself does not require compliance withXMLrules,Almost allXMLapplications are defined usingDTD.HTMLhas a standardDTDfile,its organizational structure and all tags are It is fixed. TheDTDfile is also a text file, usually with ".dtd" as its extension.

Andpoints out that theDTDused in theXMLdocument isDeclared via document type. There are two ways to declare a document type. One is to declareDTDin an external file, and the other is to declare it directly inXMLThe documentation givesDTD. (See the previous article for specific DTD content)

Element

InXMLan element consists of a start tag, element content and an end tag. Empty elements are composed of empty element tags. Each element has a type marked by a name, and it can have a set of attribute descriptions, each of which has a name and a value.

When naming elements, please note that names starting with "xml" or any other matching characters are reserved forXMLStandardization of the current or subsequent versions of the specification. In addition, you need to pay attention to the following points when naming elements:

1.The name can only use letters, underscores, or colons beginning.

2.The name cannot contain spaces.

3.Do not cause ambiguity

Comment (line 3)

Comments can help us read the document better. We can write almost any characters in the comments to help us read. However, in order to avoid ambiguity caused by the XML editor, when writing comments There are a few points that need to be noted when

1.cannot appear before theXMLstatement,XMLThe declaration must be the first part of the document.

2.Comments cannot appear within tags

3.Comments can surround and Hide the tags, but be aware that after commenting out the tags, ensure that the remaining text is still a well-structuredXMLdocument.

4.The string "--" (double connection characters) cannot appear in comments.

5.Comments ending with "--> are not allowed inXML"end.

Tips

In fact, the best way to judge whether the naming or comments are standardized is to use the browser to write the Open the XML file. If it can be opened, it means there is no problem with the naming. Otherwise, you need to modify the XML file according to the prompts until it can be opened normally with a browser.

The above is the content of XML Concise Tutorial (6). For more related content, please pay attention to the PHP Chinese website (m.sbmmt.com)!