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Semantic HTML is the use of HTML markup to reinforce the semantics, or meaning, of the information in webpages and web applications rather than merely to define its presentation or look. Semantic HTML is processed by traditional web browsers as well as by many other user agents. CSS is used to suggest its presentation to human users. As an example, recent HTML standards discourage use of the tag <i> (italic, a typeface) in preference of more accurate tags such as <em> (emphasis); the CSS stylesheet should then specify whether emphasis is denoted by an italic font, a bold font, underlining, slower or louder audible speech etc. This is because italics are used for purposes other than emphasis, such as citing a source; for this, HTML 4 provides the tag <cite>. Another use for italics is foreign phrases or loanwords; web designers may use built-in XHTML language attributes or specify their own semantic markup by choosing appropriate names for the class attribute values of HTML elements (e.g. class="loanword"). Marking emphasis, citations and loanwords in different ways makes it easier for web agents such as search engines and other software to ascertain the significance of the text.== History == HTML has included semantic markup since its inception. In an HTML document, the author may, among other things, "start with a title; add headings and paragraphs; add emphasis to () text; add images; add links to other pages; () use various kinds of lists". Various versions of the HTML standard have included presentational markup such as <font> (added in HTML 3.2; removed in HTML 4.0 Strict), <i> (all versions) and <center> (added in HTML 3.2). There are also the semantically neutral span and div tags. Since the late 1990s when Cascading Style Sheets were beginning to work in most browsers, web authors have been encouraged to avoid the use of presentational HTML markup with a view to the separation of presentation and content.〔 This article notes that presentational HTML markup may be useful when targeting browsers "before Netscape 4.0 and Internet Explorer 4.0" which were both released in 1997.〕In 2001 Tim Berners-Lee participated in a discussion of the Semantic Web, where it was presented that intelligent software 'agents' might one day automatically trawl the Web and find, filter and correlate previously unrelated, published facts for the benefit of end users. Such agents are not commonplace even now, but some of the ideas of Web 2.0, mashups and price comparison websites may be coming close. The main difference between these web application hybrids and Berners-Lee's semantic agents lies in the fact that the current aggregation and hybridisation of information is usually designed in by web developers, who already know the web locations and the API semantics of the specific data they wish to mash, compare and combine. An important type of web agent that does crawl and read web pages automatically, without prior knowledge of what it might find, is the Web crawler or search-engine spider. These software agents are dependent on the semantic clarity of web pages they find as they use various techniques and algorithms to read and index millions of web pages a day and provide web users with search facilities. In order for search-engine spiders to be able to rate the significance of pieces of text they find in HTML documents, and also for those creating mashups and other hybrids, as well as for more automated agents as they are developed, the semantic structures that exist in HTML need to be widely and uniformly applied to bring out the meaning of published text. While the true semantic web may depend on complex RDF ontologies and metadata, every HTML document makes its contribution to the meaningfulness of the Web by the correct use of headings, lists, titles and other semantic markup wherever possible. This "plain" use of HTML has been called "Plain Old Semantic HTML" or POSH. The correct use of Web 2.0 'tagging' creates folksonomies that may be equally or even more meaningful to many.〔 HTML 5 introduced new semantic tags such as section, article, footer, progress, nav, aside, mark, and time.〔(【引用サイトリンク】url=http://www.dallasseogeek.com/uncategorized/understanding-semantic-html-and-its-applications-for-2015-and-beyond/ )〕 Overall, the goal of the W3C is to slowly introduce more ways for browsers, developers, and crawlers to better distinguish between different types of data, allowing for benefits such as better display on browsers on different devices.〔Presentational markup tags are not deprecated in current HTML (4.01) and XHTML recommendations, but were recommended against. In HTML 5 some of those elements, such as i〔(【引用サイトリンク】 at=Section: 4.6.17 The i element )〕 and b〔(【引用サイトリンク】 at=Section: 4.6.18 The b element )〕 are still specified as their meaning has been clearly defined "as to be stylistically offset from the normal prose without conveying any extra importance".抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Semantic HTML」の詳細全文を読む スポンサード リンク
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