Currently , HTML5 is still a draft specification, and is not yet an official standard. However, it is already widely supported by browsers and other web-enabled devices, and is the way of the future. Therefore, HTML5 is the primary language taught in this course. The following table shows a list of many of the types of content that can be added to web pages using different versions of HTML. XHTML 2 takes a completely different approach, by taking the premise that all images have a long description and treating the image and the text as equivalents.
In XHTML 2 any element may have a src attribute, which specifies a resource such as an image to load instead of the element. If the resource is unavailable because of network failure, because it is of a type that the browser can't handle, or because images have been turned off then the element is used instead.
Essentially the longdesc has been moved into the document, though this behavior also mimicks the fallback behavior of the object element. To achieve the tooltip effect that some browsers gave with the alt attribute, as in HTML 4 you use the title attribute.
Events: event handling in HTML was restricted in several ways: since the event names were hard-wired in the language such as onclick , the only way to add new events was to change the language; many of the events such as click were device-specific, rather than referring to the intent of the event such as activating a link ; you could only handle an event in one scripting language — it was not possible to supply event handlers in the same document for several different scripting languages.
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Isindex C. The lang and xml:lang Attributes C. Fragment Identifiers C. Character Encoding C. Boolean Attributes C. XML C. References 1. This section is informative. XHTML 1. It is intended to be used as a language for content that is both XML-conforming and, if some simple guidelines are followed, operates in HTML 4 conforming user agents.
By migrating to XHTML today, content developers can enter the XML world with all of its attendant benefits, while still remaining confident in their content's backward and future compatibility.
SGML is a language for describing markup languages, particularly those used in electronic document exchange, document management, and document publishing. SGML has been around since the middle 's and has remained quite stable. Much of this stability stems from the fact that the language is both feature-rich and flexible. This flexibility, however, comes at a price, and that price is a level of complexity that has inhibited its adoption in a diversity of environments, including the World Wide Web.
HTML, as originally conceived, was to be a language for the exchange of scientific and other technical documents, suitable for use by non-document specialists. HTML addressed the problem of SGML complexity by specifying a small set of structural and semantic tags suitable for authoring relatively simple documents.
In addition to simplifying the document structure, HTML added support for hypertext. Multimedia capabilities were added later. In a remarkably short space of time, HTML became wildly popular and rapidly outgrew its original purpose.
This plethora of new elements has led to interoperability problems for documents across different platforms. While retaining these beneficial features, XML removes many of the more complex features of SGML that make the authoring and design of suitable software both difficult and costly.
The following terms are used in this specification. See Section 3. Such a document must meet all of the following criteria:. An example root element might look like:. The system identifier may be changed to reflect local system conventions. Such a declaration is required when the character encoding of the document is other than the default UTF-8 or UTF and no encoding was determined by a higher-level protocol.
In this example, the XML declaration is included. Work by W3C is addressing ways to specify conformance for documents involving multiple namespaces. White space is handled according to the following rules. The following characters are defined in [ XML ] white space characters:. Note that the CSS2 recommendation does not explicitly address the issue of whitespace handling in non-Latin character sets.
This will be addressed in a future version of CSS, at which time this reference will be updated. Well-formedness is a new concept introduced by [ XML ].
Essentially this means that all elements must either have closing tags or be written in a special form as described below , and that all the elements must nest properly.
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