13 This is often referred to as a separation of concerns. Html is used to represent the structure or content of a document, its presentation remains the sole responsibility of css style sheets. A default style sheet is suggested as part of the css standard, giving a default rendering for html. 14 Behavior (interactivity) is also kept separate from content, and is handled by scripts. Images are contained in separate graphics files, separate from text, though they can also be considered part of the content of a page. Separation of concerns allows the document to be presented by different user agents according to their purposes and abilities. For example, a user agent can select an appropriate style sheet to present a document by displaying on a monitor, printing on paper, or to determine speech characteristics in an audio-only user agent.
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The elements in each are identical, and in most cases valid xhtml.0 documents will be valid or nearly valid html.01 documents. This article mainly focuses on real html, unless noted otherwise; however, it remains applicable to xhtml. See html for a discussion homework of the minor differences between the two. Element status edit since the first version of html, several elements have become outmoded, and are deprecated in later standards, or do not appear at all, in which food case they are invalid (and will be found invalid, and perhaps not displayed, by validating user agents). 11 At present, the status of elements is complicated by the existence of three types of html.01 / xhtml.0 dtd : Transitional, which contain deprecated elements, but which were intended to provide a transitional period during which authors could update their practices; Frameset. The first Standard ( html.0 ) contained four deprecated elements, one of which was invalid in html.2. All four are invalid in html.01 Transitional, which also deprecated a further ten elements. All of these, plus two others, are invalid in html.01 Strict. While the frame elements are still current in the sense of being present in the Transitional and Frameset dtds, there are no plans to preserve them in future standards, as their function has been largely replaced, and they are highly problematic for user accessibility. (Strictly speaking, the most recent xhtml standard, xhtml.1 (2001 does not include frames at all; it is approximately equivalent to xhtml.0 Strict, but also includes the ruby markup module.) 12 A common source of confusion is the loose use of deprecated to refer. Presentation and behavior edit since html 4, html has increasingly focused on the separation of content (the visible text and images) from presentation (like color, font size, and layout).
Element (and attribute) names may be written in any combination of upper or lower case in html, but must be in lower case in xhtml. 9 The canonical form was upper-case until html 4, and was used in html specifications, but in recent years, lower-case has become more common. Element standards edit html elements are defined in a series of freely available open standards issued since 1995, initially by the ietf and subsequently by the W3C. During the browser wars of the 1990s, developers of user agents (e.g. Web browsers ) biography often developed their own elements, some of which have been adopted in later standards. Other user agents may not recognize non-standard elements, and they will be ignored, possibly causing the page to be displayed improperly. In 1998, xml (a simplified form of sgml) introduced mechanisms to allow anyone to develop their own elements and incorporate them in xhtml documents, for use with xml-aware user agents. 10 Subsequently, html.01 was rewritten in an xml -compatible form, xhtml.0 ( eXtensible html ).
The end tag is required in xhtml. example needed normal elements usually have both a start report tag and an end tag, although for some elements the end tag, or both tags, can be omitted. It is constructed in a similar way: a start tag ( tag ) marking the beginning of an element, which may incorporate any number of html attributes ; some amount of content, including text and other elements; an end tag, in which the element name. Html attributes define desired behavior or indicate additional element properties. Most attributes require a value. In html, the value can be left u"d if it doesn't include spaces (namevalue or it can be"d with single or double"s (name'value' or name"value. In xml, those"s are required. Boolean attributes, on the other hand, don't require a value to be specified. An example is the checked for checkboxes: input typecheckbox checked In the xml syntax, though, the name should be repeated as the value: input type"checkbox" checked"checked" / Informally, html elements are sometimes referred to as "tags" (an example of synecdoche though many prefer the term.
Void elements only have a start tag, which contains any html attributes. They may not contain any children, such as text or other elements. Often they are place holders for elements which reference external files, such as the image ( img / ) element. The attributes included in the element will then point to the external file in question. Another example of a void element is the link / element, for which the syntax is: link rel"stylesheet" href"s" type"text/css" This link / element points the browser at a style sheet to use when presenting the html document to the user. Note that in the html syntax, attributes don't have to be"d if they are composed only of certain characters: letters, digits, the hyphen-minus and the full stop. When using the xml syntax ( xhtml on the other hand, all attributes must be"d, and a trailing slash is required before the last angle bracket: link rel"stylesheet" href"s" type"text/css" / raw text elements are constructed with: a start tag ( tag ) marking. In some versions of html, the end tag is optional for some elements.
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mathsf End atop tag mathsf Element Parts of an html container element In the html syntax, most elements are written with a start tag and an end tag, with the content in between. An html tag is composed of the name of the element, surrounded by angle brackets. An end tag also has a slash after the opening angle bracket, to distinguish it from the start tag. For example, a paragraph, which is represented by the p element, would be written as: p In the html syntax, most elements are written. p however, not all of these elements require the end tag, or even the start tag, to be present. Some elements, resume the so-called void elements or empty elements, do not have an end tag. A typical example is the br / element, which represents a significant line break, such as in a poem or an address.
A void element's behavior is predefined, and it cannot contain any content or other elements. For example, an address would be written as:. Sherman br 42 Wallaby way br Sydney /p When using an xhtml dtd, it is required to open and close the element with a single tag. To specify that it is a void element, a / is included at the end of the tag (not to be confused with the / at the beginning of a closing tag). Sherman br / 42 Wallaby way br / Sydney /p html attributes are specified inside the start tag. For example, the abbr element, which represents an abbreviation, expects a title attribute within its opening tag. This would be written as: abbr There are multiple kinds of html elements: void elements, raw text elements, and normal elements.
This is applied to those elements that css considers to be "block" elements, set through the css display: block; declaration. Html also has a similar concept, although different, and the two are very frequently confused. Block; and inline; are groups within the html dtd that group elements as being either "block-level" or "inline". 7 This is used to define their nesting behavior: block-level elements cannot be placed into an inline context. Note 7 This behavior cannot be changed; it is fixed in the dtd. Block and inline elements have the appropriate and different css behaviors attached to them by default, 7 including the relevance of the box model for particular element types.
Note though that this css behavior can, and frequently is, changed from the default. Lists with. Are block; elements and are presented as block elements by default. However, it is quite common to set these with css to display as an inline list. 8 overview edit syntax edit p tagThis is a overbrace overbrace mathtt color BrickRed! P color Magentaunderbrace mathtt class _mathsf color BlackAttribute atop namemathtt! Underbrace mathtt foo _mathsf color WhiteAttr atop color Blackvalue mathtt color BrickRed mathsf Start tagoverbrace mathtt color GreenThis is a paragraph. Mathsf Contentoverbrace mathtt color BrickRed!/p!
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Xml parsing is simpler. The relation from tags to elements is always like that of parsing the actual tags included in the document, without the implied closures that are part of sgml. Note 5 In Macros html can be formed as xml, either through xhtml or through html5, the parsing of document tags as dom elements is simplified. Once the dom of elements is obtained, behavior beyond that point (i.e. Screen rendering) is identical. Note 6 block;. Box edit part of this css presentation behavior is the notion of the " box model ".
5 note 4 The dtd specifies which element types are possible (i.e. It defines the set of element types that go to make up html) and it also specifies the valid combinations in which they may appear in a document. It is part of general sgml behavior that where only one valid structure is possible (per the dtd it is not generally a requirement that the document explicitly states that structure. As a simple example, impression the p start tag indicating the start of a paragraph element should be closed by a /p end tag, indicating the end of the element. Also the dtd states that paragraph elements cannot be nested. The html document fragment: p Para 1 p Para 2 p Para 3 can thus be inferred to be equivalent to: p Para 1 /p p Para 2 /p p Para 3 (If one paragraph element cannot contain another, any currently open paragraph must. Xml edit sgml is complex, which has limited its widespread adoption and understanding. Xml was developed as a simpler alternative. Xml is similar to sgml, that can also use the dtd mechanism to specify the supported elements and their permitted combinations as document structure.
the " tag soup " supplied had been. Only in the rarest cases would the parser abandon parsing altogether. Tags edit "Elements" and "tags" are terms that are widely confused. Html documents contain tags, but do not contain the elements. The elements are only generated after the parsing step, from these tags. Citation needed As is generally understood, the position of an element is indicated as spanning from a start tag, possibly including some child content, and is terminated by an end tag. 3 This is the case for many, but not all, elements within an html document. As html is based on sgml, 4 its parsing also depends on the use of a dtd, specifically an html dtd such as that for html.01.
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This article is about the, html elements in general. For information on how to format wikipedia entries, see. Help:wiki markup and, help:html in wikitext. For the chemical compound nobr, see. An, html element is an individual component. Html document or web page, once this has been proposal parsed into the. Html is composed of a tree of html nodes, such as text nodes. Each node can have. Nodes can also have content, including other nodes and text.