History of HTML
- Initially work on HTML was started in 1989 by Tim Berners Lee.
- In 1995, HTML 2.0 was published by IETF (Internet Engineering Task Force). HTML 2.0 is the first standard HTML specification.
- In 1997, HTML 3.2 was published by W3C (World Wide Web Consortium).
- In 1997, HTML 4.0 was published by W3C. It provides three variations: strict, transitional and frameset.
- In 1999, HTML 4.01 was published by W3C.
- HTML 5 was published in October, 2014
HTML Values and Units
HTML Syntax
The basic syntactic units in any HTML document are: tags, elements and attributes. HTML describes information in a web document with the help of tags, which provide a way for marking the text. The syntax of a tag is shown below:
< tag-name >
For example, using HTML, we can display paragraphs in a web document using the <p> tag. Every browser will have default presentation effects for each tag. Almost all of the tags are written in pairs (a opening tag and a closing tag) as shown below:
< tag-name > content here…. </ tag-name >
In HTML, the content in a web document is described using the tags. The collection of content and the enclosing tags is known as an element. For example, a paragraph element looks as shown below:
<p> This is a paragraph… </p>
In general, all tags in HTML support attributes using which additional information is specified to the browser to render the content of the element. For example, an old way of aligning the text in a paragraph to the center of the document is shown below:
<p align=”center”>This is a paragraph…</p>
In the above example, align is the attribute-name and center is its value. General syntax for writing attributes is:
attribute-name = “value”
Text and Comments
HTML comments can be used by the developer of the web pages to document certain sections in the web page. A comment in HTML should be written as follows:
<!– Your comment here. –>
Comments are generally used for short text, not for commenting out large sections of HTML code. The text included in the comments is not visible to the user.
CDATA Sections
For larger comment sections, CDATA (character data) sections can be used. CDATA structures are also useful in XML and XHTML. The format for the CDATA tag is as follows:
<![CDATA[ Commented text goes here. ]]>
Both comments and CDATA tags cannot be nested.
The term CDATA is used about text data that should not be parsed by the XML parser. Characters like “<” and “&” are illegal in XML elements. “<” will generate an error because the parser interprets it as the start of a new element. “&” will generate an error because the parser interprets it as the start of a character entity.
Some text, like JavaScript code, contains a lot of “<” or “&” characters. To avoid errors, script code can be defined as CDATA. Everything inside a CDATA section is ignored by the parser. A CDATA section starts with “<![CDATA[” and ends with “]]>“.
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