Web page Standard Beginner: What is XHTML?

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　　What is XHTML?

XHTML is a series of current and future document types and program blocks, which are regenerated and extended by HTML 4 [HTML], and HTML 4 is a subset of them. XHTML series documents are based on XML and are ultimately designed to work with xml-based user agents. Details of the XHTML family and their development process are detailed in the future Trends section.

XHTML 1.0 (This specification book) is the first document of the XHTML family. It was 1.0 after applying 3 kinds of HTML 4 document types to XML (XML). The intention is that, as a language, its content conforms to XML and can be identified by HTML4 user agents if they follow a few simple guidelines. Developers will be able to transplant their documents into XHTML 1.0, with the following benefits:

XHTML documents conform to XML. This makes it easy to view, edit, and validate them with standard XML tools.

XHTML documents can be used in existing HTML4 proxy user programs, or they can be used in new XHTML user agents, which can achieve the same or better effect as the former.

Applications used in XHTML documents, such as script and applets, can be either the Document Object model of HTML or the Document Object model of XML [DOM].

With the development of the XHTML family, documents conforming to XHTML 1.0 are more likely to be used in a variety of XHTML environments.

The XHTML family is the next step in the development of the Internet. By porting documents to XML now, developers can also enjoy the benefits of entering the XML world while ensuring that their documents are compatible.

　　What is HTML 4?

HTML 4 [HTML] is an application of SGML (Standard generalized Markup Language) that complies with ISO 8879 and is widely used as the standard publishing language on the World Wide Web.

SGML is a language that describes markup languages, especially those used in electronic document exchange, document management, and document publishing languages. HTML is an instance of the language defined by SGML.

SGML appeared in the middle of the 80 and has remained stable. Stability is the result of its rich characteristics and flexibility. However, flexibility brings a degree of complexity that limits its adaptability in a variety of environments, including the world Wide Web.

HTML was originally conceived as a language for exchanging scientific and other technical documents for use by experts unfamiliar with writing documents. HTML provides a small set of structural semantic tags that are suitable for writing relatively simple documents, thus solving the problem of SGML complexity. In addition to simplifying the document structure, HTML also adds support for hypertext, adding media capabilities later.

In a very short time, HTML became widely popular and quickly exceeded its original purpose. The new elements within the HTML (standard) are created quickly, and HTML is quickly adapted for use in vertical, highly specialized markets. Additional new elements result in a document compatibility issue across platforms.

As software and platform inconsistencies increase, it is clear that the applicability of "classic" HTML 4 on these platforms is limited.

　　What is XML?

Xml™[xml] is the abbreviation of Extensible Markup Language, the purpose of which is to regain the ability and flexibility of SGML and remove most of its complexity. Although a restricted SGML form, XML retains most of the functionality and richness of SGML, and retains all the common features of SGML.

While preserving these useful features, XML removes many of the more complex features of SMGL, which make it difficult and expensive to write and design the right software.

　　Why do I need XHTML?

The benefits of porting to XHTML have been mentioned above, and in general, the benefits of porting to XHTML are:

Document developers and user agent programmers often use new methods, new tags to express their ideas. It is relatively easy to import new elements and new element attributes with XML. The XHTML family is designed to provide these extensions, through XHTML modules and the development of new XHTML-compliant modules. (will be described in the upcoming XHTML modular specification). These modules will allow you to mix existing and new feature sets when developing documents and designing new user agents.

Various alternative ways of accessing the Internet are constantly being presented. Some people estimate that by 2002, 75% of documents on the Internet will be viewed on these alternative platforms. XHTML is designed to take into account the collaborative work of user agents. With a new user agent and document protocol mechanism, servers, agents, and user agents will be able to best meet the transmission, and finally, it is possible to develop documents that follow XHTML and be used by any user agent that adheres to XHTML.