


XMLThe namespace indicates the usage range of XML names. Because XML can customize element tags, there is a high chance that XML names will overlap between different XML applications.
Without a way to differentiate between names that don't apply, confusion would result. XML namespaces are designed to solve this problem. Through the XML namespace, we can distinguish the XML names from different XML applications. very big. Without a way to differentiate between names that don't apply, confusion would result. XML namespaces are designed to solve this problem. Through XML namespaces, we can distinguish elements and attributes with the same name from different XML applications. Related elements and attributes from a single XML application can be grouped together to facilitate software identification and processing.
Namespaces are grouped by prefix and local , separated by colons. The prefix identifies the namespace in which the element or attribute resides, and the local part identifies an element or attribute within the namespace. The entire name is also called a qualified name (qual
ified name). The prefix can be composed of any legal XML name characters except the three letters of XML (in any combination of upper and lower case). Each prefix in a qualified name must be associated with a unique URI. Names associated with the same URI prefix belong to the same namespace. <rdf:RDF xmlns:rdf="http://www.w3.org/TR/REC-rdf-syntax#">
<rdf:Description about="http://www.example.com/test.xml">
<title>example</title>
<author>linuxsir</author> ... </rdf:Description>
</rdf:RDF>
The prefix is generally defined in the top-level element using the prefix. Different prefixes can also be defined in lower-level elements:
<rdf:RDF xmlns:rdf="http://www.w3.org/TR/REC-rdf-syntax#"> <rdf:Description xmlns:dc="http://www.w3.org/dc/" about="http://www.example.com/test.xml"> <dc:title>example</dc:title> <dc:author>linuxsir</dc:author> ... </rdf:Description> </rdf:RDF>
By appending the unprefixed xmlns attribute to the root element, you can specify that the element without the prefix and all the child elements without the prefix belong to a certain namespace.
<svg xmlns="http://www.w3.org/2000/svg"> <ellipse rx="110" ry="130" /> <rect x="4cm" y="1cm" /> </svg>
If the namespace is only used to identify elements and attributes from a certain XML application, and is not used to distinguish different elements with the same name, it can be used in
DTD
<!ATTLIST svg xmlns CDATA #FIXED "http://www.w3.org/svg/">
When defining a DTD, if you need to use a namespace prefix, you must also write the prefix into the DTD definition when defining, such as:
<!ELEMENT xlink:name (#PCDATA)>
Using parameter entities Reference
to define the namespace prefix can facilitate the maintenance, organization and release of DTD documents! Please indicate the source when reprinting, thank you! <!ENTITY % prefix "xlink"> <!ENTITY % colon ":">
Then, use the parameter entity name to define more parameter entity references, such as:
<!ENTITY % xlink-title "%prefix;%colon;title"> <!ENTITY % xlink-author "%prefix;%colon;author">
In this way, if you need to change the prefix, You only need to modify one place, not the entire document.
<!ELEMENT %xlink-title; (#PCDATA)> <!ELEMENT %xlink-author; (#PCDATA)> 不能在ATTLIST和ELEMENT声明中直接使用%prefix;和%colon;, 因为在另一个实体的外部使用这些参数实体时,XML解析器会在实体替换文本的两边添加额外的空格。
The above is the detailed content of XML introductory tutorial-detailed introduction to XML namespaces. For more information, please follow other related articles on the PHP Chinese website!

RSS and XML are tools for web content management. RSS is used to publish and subscribe to content, and XML is used to store and transfer data. They work with content publishing, subscriptions, and update push. Examples of usage include RSS publishing blog posts and XML storing book information.

RSS documents are XML-based structured files used to publish and subscribe to frequently updated content. Its main functions include: 1) automated content updates, 2) content aggregation, and 3) improving browsing efficiency. Through RSSfeed, users can subscribe and get the latest information from different sources in a timely manner.

The XML structure of RSS includes: 1. XML declaration and RSS version, 2. Channel (Channel), 3. Item. These parts form the basis of RSS files, allowing users to obtain and process content information by parsing XML data.

RSSfeedsuseXMLtosyndicatecontent;parsingtheminvolvesloadingXML,navigatingitsstructure,andextractingdata.Applicationsincludebuildingnewsaggregatorsandtrackingpodcastepisodes.

RSS documents work by publishing content updates through XML files, and users subscribe and receive notifications through RSS readers. 1. Content publisher creates and updates RSS documents. 2. The RSS reader regularly accesses and parses XML files. 3. Users browse and read updated content. Example of usage: Subscribe to TechCrunch's RSS feed, just copy the link to the RSS reader.

The steps to build an RSSfeed using XML are as follows: 1. Create the root element and set the version; 2. Add the channel element and its basic information; 3. Add the entry element, including the title, link and description; 4. Convert the XML structure to a string and output it. With these steps, you can create a valid RSSfeed from scratch and enhance its functionality by adding additional elements such as release date and author information.

The steps to create an RSS document are as follows: 1. Write in XML format, with the root element, including the elements. 2. Add, etc. elements to describe channel information. 3. Add elements, each representing a content entry, including,,,,,,,,,,,. 4. Optionally add and elements to enrich the content. 5. Ensure the XML format is correct, use online tools to verify, optimize performance and keep content updated.

The core role of XML in RSS is to provide a standardized and flexible data format. 1. The structure and markup language characteristics of XML make it suitable for data exchange and storage. 2. RSS uses XML to create a standardized format to facilitate content sharing. 3. The application of XML in RSS includes elements that define feed content, such as title and release date. 4. Advantages include standardization and scalability, and challenges include document verbose and strict syntax requirements. 5. Best practices include validating XML validity, keeping it simple, using CDATA, and regularly updating.


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